************************************************************************
* This file is part of OpenMolcas.                                     *
*                                                                      *
* OpenMolcas is free software; you can redistribute it and/or modify   *
* it under the terms of the GNU Lesser General Public License, v. 2.1. *
* OpenMolcas is distributed in the hope that it will be useful, but it *
* is provided "as is" and without any express or implied warranties.   *
* For more details see the full text of the license in the file        *
* LICENSE or in <http://www.gnu.org/licenses/>.                        *
************************************************************************
      subroutine dqag(f,a,b,epsabs,epsrel,key,result,abserr,neval,ier,
     *    limit,lenw,last,iwork,work)
c***begin prologue  dqag
c***date written   800101   (yymmdd)
c***revision date  830518   (yymmdd)
c***category no.  h2a1a1
c***keywords  automatic integrator, general-purpose,
c             integrand examinator, globally adaptive,
c             gauss-kronrod
c***author  piessens,robert,appl. math. & progr. div - k.u.leuven
c           de doncker,elise,appl. math. & progr. div. - k.u.leuven
c***purpose  the routine calculates an approximation result to a given
c            definite integral i = integral of f over (a,b),
c            hopefully satisfying following claim for accuracy
c            abs(i-result)le.max(epsabs,epsrel*abs(i)).
c***description
c
c        computation of a definite integral
c        standard fortran subroutine
c        real*8 version
c
c            f      - real*8
c                     function subprogam defining the integrand
c                     function f(x). the actual name for f needs to be
c                     declared e x t e r n a l in the driver program.
c
c            a      - real*8
c                     lower limit of integration
c
c            b      - real*8
c                     upper limit of integration
c
c            epsabs - real*8
c                     absolute accoracy requested
c            epsrel - real*8
c                     relative accuracy requested
c                     if  epsabs.le.0
c                     and epsrel.lt.max(50*rel.mach.acc.,0.5d-28),
c                     the routine will end with ier = 6.
c
c            key    - integer
c                     key for choice of local integration rule
c                     a gauss-kronrod pair is used with
c                       7 - 15 points if key.lt.2,
c                      10 - 21 points if key = 2,
c                      15 - 31 points if key = 3,
c                      20 - 41 points if key = 4,
c                      25 - 51 points if key = 5,
c                      30 - 61 points if key.gt.5.
c
c         on return
c            result - real*8
c                     approximation to the integral
c
c            abserr - real*8
c                     estimate of the modulus of the absolute error,
c                     which should equal or exceed abs(i-result)
c
c            neval  - integer
c                     number of integrand evaluations
c
c            ier    - integer
c                     ier = 0 normal and reliable termination of the
c                             routine. it is assumed that the requested
c                             accuracy has been achieved.
c                     ier.gt.0 abnormal termination of the routine
c                             the estimates for result and error are
c                             less reliable. it is assumed that the
c                             requested accuracy has not been achieved.
c                      error messages
c                     ier = 1 maximum number of subdivisions allowed
c                             has been achieved. one can allow more
c                             subdivisions by increasing the value of
c                             limit (and taking the according dimension
c                             adjustments into account). however, if
c                             this yield no improvement it is advised
c                             to analyze the integrand in order to
c                             determine the integration difficulaties.
c                             if the position of a local difficulty can
c                             be determined (i.e.singularity,
c                             discontinuity within the interval) one
c                             will probably gain from splitting up the
c                             interval at this point and calling the
c                             integrator on the subranges. if possible,
c                             an appropriate special-purpose integrator
c                             should be used which is designed for
c                             handling the type of difficulty involved.
c                         = 2 the occurrence of roundoff error is
c                             detected, which prevents the requested
c                             tolerance from being achieved.
c                         = 3 extremely bad integrand behaviour occurs
c                             at some points of the integration
c                             interval.
c                         = 6 the input is invalid, because
c                             (epsabs.le.0 and
c                              epsrel.lt.max(50*rel.mach.acc.,0.5d-28))
c                             or limit.lt.1 or lenw.lt.limit*4.
c                             result, abserr, neval, last are set
c                             to zero.
c                             except when lenw is invalid, iwork(1),
c                             work(limit*2+1) and work(limit*3+1) are
c                             set to zero, work(1) is set to a and
c                             work(limit+1) to b.
c
c         dimensioning parameters
c            limit - integer
c                    dimensioning parameter for iwork
c                    limit determines the maximum number of subintervals
c                    in the partition of the given integration interval
c                    (a,b), limit.ge.1.
c                    if limit.lt.1, the routine will end with ier = 6.
c
c            lenw  - integer
c                    dimensioning parameter for work
c                    lenw must be at least limit*4.
c                    if lenw.lt.limit*4, the routine will end with
c                    ier = 6.
c
c            last  - integer
c                    on return, last equals the number of subintervals
c                    produced in the subdiviosion process, which
c                    determines the number of significant elements
c                    actually in the work arrays.
c
c         work arrays
c            iwork - integer
c                    vector of dimension at least limit, the first k
c                    elements of which contain pointers to the error
c                    estimates over the subintervals, such that
c                    work(limit*3+iwork(1)),... , work(limit*3+iwork(k))
c                    form a decreasing sequence with k = last if
c                    last.le.(limit/2+2), and k = limit+1-last otherwise
c
c            work  - real*8
c                    vector of dimension at least lenw
c                    on return
c                    work(1), ..., work(last) contain the left end
c                    points of the subintervals in the partition of
c                     (a,b),
c                    work(limit+1), ..., work(limit+last) contain the
c                     right end points,
c                    work(limit*2+1), ..., work(limit*2+last) contain
c                     the integral approximations over the subintervals,
c                    work(limit*3+1), ..., work(limit*3+last) contain
c                     the error estimates.
c
c***references  (none)
c***routines called  dqage,xerror
c***end prologue  dqag
      real*8 a,abserr,b,epsabs,epsrel,f,result,work
      integer ier,iwork,key,last,lenw,limit,lvl,l1,l2,l3,neval
c
      dimension iwork(limit),work(lenw)
c
      external f
c
c         check validity of lenw.
c
c***first executable statement  dqag
      ier = 6
      neval = 0
      last = 0
      result = 0.0d+00
      abserr = 0.0d+00
      if(limit.lt.1.or.lenw.lt.limit*4) go to 10
c
c         prepare call for dqage.
c
      l1 = limit+1
      l2 = limit+l1
      l3 = limit+l2
c
      call dqage(f,a,b,epsabs,epsrel,key,limit,result,abserr,neval,
     *  ier,work(1),work(l1),work(l2),work(l3),iwork,last)
c
c         call error handler if necessary.
c
      lvl = 0
10    if(ier.eq.6) lvl = 1
      if(ier.ne.0) call xerror('abnormal return from dqag ',26,ier,lvl)
      return
      end
      subroutine dqage(f,a,b,epsabs,epsrel,key,limit,result,abserr,
     *   neval,ier,alist,blist,rlist,elist,iord,last)
c***begin prologue  dqage
c***date written   800101   (yymmdd)
c***revision date  830518   (yymmdd)
c***category no.  h2a1a1
c***keywords  automatic integrator, general-purpose,
c             integrand examinator, globally adaptive,
c             gauss-kronrod
c***author  piessens,robert,appl. math. & progr. div. - k.u.leuven
c           de doncker,elise,appl. math. & progr. div. - k.u.leuven
c***purpose  the routine calculates an approximation result to a given
c            definite integral   i = integral of f over (a,b),
c            hopefully satisfying following claim for accuracy
c            abs(i-reslt).le.max(epsabs,epsrel*abs(i)).
c***description
c
c        computation of a definite integral
c        standard fortran subroutine
c        real*8 version
c
c        parameters
c         on entry
c            f      - real*8
c                     function subprogram defining the integrand
c                     function f(x). the actual name for f needs to be
c                     declared e x t e r n a l in the driver program.
c
c            a      - real*8
c                     lower limit of integration
c
c            b      - real*8
c                     upper limit of integration
c
c            epsabs - real*8
c                     absolute accuracy requested
c            epsrel - real*8
c                     relative accuracy requested
c                     if  epsabs.le.0
c                     and epsrel.lt.max(50*rel.mach.acc.,0.5d-28),
c                     the routine will end with ier = 6.
c
c            key    - integer
c                     key for choice of local integration rule
c                     a gauss-kronrod pair is used with
c                          7 - 15 points if key.lt.2,
c                         10 - 21 points if key = 2,
c                         15 - 31 points if key = 3,
c                         20 - 41 points if key = 4,
c                         25 - 51 points if key = 5,
c                         30 - 61 points if key.gt.5.
c
c            limit  - integer
c                     gives an upperbound on the number of subintervals
c                     in the partition of (a,b), limit.ge.1.
c
c         on return
c            result - real*8
c                     approximation to the integral
c
c            abserr - real*8
c                     estimate of the modulus of the absolute error,
c                     which should equal or exceed abs(i-result)
c
c            neval  - integer
c                     number of integrand evaluations
c
c            ier    - integer
c                     ier = 0 normal and reliable termination of the
c                             routine. it is assumed that the requested
c                             accuracy has been achieved.
c                     ier.gt.0 abnormal termination of the routine
c                             the estimates for result and error are
c                             less reliable. it is assumed that the
c                             requested accuracy has not been achieved.
c            error messages
c                     ier = 1 maximum number of subdivisions allowed
c                             has been achieved. one can allow more
c                             subdivisions by increasing the value
c                             of limit.
c                             however, if this yields no improvement it
c                             is rather advised to analyze the integrand
c                             in order to determine the integration
c                             difficulties. if the position of a local
c                             difficulty can be determined(e.g.
c                             singularity, discontinuity within the
c                             interval) one will probably gain from
c                             splitting up the interval at this point
c                             and calling the integrator on the
c                             subranges. if possible, an appropriate
c                             special-purpose integrator should be used
c                             which is designed for handling the type of
c                             difficulty involved.
c                         = 2 the occurrence of roundoff error is
c                             detected, which prevents the requested
c                             tolerance from being achieved.
c                         = 3 extremely bad integrand behaviour occurs
c                             at some points of the integration
c                             interval.
c                         = 6 the input is invalid, because
c                             (epsabs.le.0 and
c                              epsrel.lt.max(50*rel.mach.acc.,0.5d-28),
c                             result, abserr, neval, last, rlist(1) ,
c                             elist(1) and iord(1) are set to zero.
c                             alist(1) and blist(1) are set to a and b
c                             respectively.
c
c            alist   - real*8
c                      vector of dimension at least limit, the first
c                       last  elements of which are the left
c                      end points of the subintervals in the partition
c                      of the given integration range (a,b)
c
c            blist   - real*8
c                      vector of dimension at least limit, the first
c                       last  elements of which are the right
c                      end points of the subintervals in the partition
c                      of the given integration range (a,b)
c
c            rlist   - real*8
c                      vector of dimension at least limit, the first
c                       last  elements of which are the
c                      integral approximations on the subintervals
c
c            elist   - real*8
c                      vector of dimension at least limit, the first
c                       last  elements of which are the moduli of the
c                      absolute error estimates on the subintervals
c
c            iord    - integer
c                      vector of dimension at least limit, the first k
c                      elements of which are pointers to the
c                      error estimates over the subintervals,
c                      such that elist(iord(1)), ...,
c                      elist(iord(k)) form a decreasing sequence,
c                      with k = last if last.le.(limit/2+2), and
c                      k = limit+1-last otherwise
c
c            last    - integer
c                      number of subintervals actually produced in the
c                      subdivision process
c
c***references  (none)
c***routines called  d1mach,dqk15,dqk21,dqk31,
c                    dqk41,dqk51,dqk61,dqpsrt
c***end prologue  dqage
c
      real*8 a,abserr,alist,area,area1,area12,area2,a1,a2,b,
     *  blist,b1,b2,defabs,defab1,defab2,d1mach,elist,epmach,
     *  epsabs,epsrel,errbnd,errmax,error1,error2,erro12,errsum,f,
     *  resabs,result,rlist,uflow
      integer ier,iord,iroff1,iroff2,k,key,keyf,last,limit,maxerr,neval,
     *  nrmax
c
      dimension alist(limit),blist(limit),elist(limit),iord(limit),
     *  rlist(limit)
c
      external f
c
c            list of major variables
c            -----------------------
c
c           alist     - list of left end points of all subintervals
c                       considered up to now
c           blist     - list of right end points of all subintervals
c                       considered up to now
c           rlist(i)  - approximation to the integral over
c                      (alist(i),blist(i))
c           elist(i)  - error estimate applying to rlist(i)
c           maxerr    - pointer to the interval with largest
c                       error estimate
c           errmax    - elist(maxerr)
c           area      - sum of the integrals over the subintervals
c           errsum    - sum of the errors over the subintervals
c           errbnd    - requested accuracy max(epsabs,epsrel*
c                       abs(result))
c           *****1    - variable for the left subinterval
c           *****2    - variable for the right subinterval
c           last      - index for subdivision
c
c
c           machine dependent constants
c           ---------------------------
c
c           epmach  is the largest relative spacing.
c           uflow  is the smallest positive magnitude.
c
c***first executable statement  dqage
      epmach = d1mach(4)
      uflow = d1mach(1)
c
c           test on validity of parameters
c           ------------------------------
c
      ier = 0
      neval = 0
      last = 0
      result = 0.0d+00
      abserr = 0.0d+00
      alist(1) = a
      blist(1) = b
      rlist(1) = 0.0d+00
      elist(1) = 0.0d+00
      iord(1) = 0
      if(epsabs.le.0.0d+00.and.
     *  epsrel.lt.max(0.5d+02*epmach,0.5d-28)) ier = 6
      if(ier.eq.6) go to 999
c
c           first approximation to the integral
c           -----------------------------------
c
      keyf = key
      if(key.le.0) keyf = 1
      if(key.ge.7) keyf = 6
      neval = 0
      if(keyf.eq.1) call dqk15(f,a,b,result,abserr,defabs,resabs)
      if(keyf.eq.2) call dqk21(f,a,b,result,abserr,defabs,resabs)
      if(keyf.eq.3) call dqk31(f,a,b,result,abserr,defabs,resabs)
      if(keyf.eq.4) call dqk41(f,a,b,result,abserr,defabs,resabs)
      if(keyf.eq.5) call dqk51(f,a,b,result,abserr,defabs,resabs)
      if(keyf.eq.6) call dqk61(f,a,b,result,abserr,defabs,resabs)
      last = 1
      rlist(1) = result
      elist(1) = abserr
      iord(1) = 1
c
c           test on accuracy.
c
      errbnd = max(epsabs,epsrel*abs(result))
      if(abserr.le.0.5d+02*epmach*defabs.and.abserr.gt.errbnd) ier = 2
      if(limit.eq.1) ier = 1
      if(ier.ne.0.or.(abserr.le.errbnd.and.abserr.ne.resabs)
     *  .or.abserr.eq.0.0d+00) go to 60
c
c           initialization
c           --------------
c
c
      errmax = abserr
      maxerr = 1
      area = result
      errsum = abserr
      nrmax = 1
      iroff1 = 0
      iroff2 = 0
c
c           main do-loop
c           ------------
c
      do 30 last = 2,limit
c
c           bisect the subinterval with the largest error estimate.
c
        a1 = alist(maxerr)
        b1 = 0.5d+00*(alist(maxerr)+blist(maxerr))
        a2 = b1
        b2 = blist(maxerr)
        if(keyf.eq.1) call dqk15(f,a1,b1,area1,error1,resabs,defab1)
        if(keyf.eq.2) call dqk21(f,a1,b1,area1,error1,resabs,defab1)
        if(keyf.eq.3) call dqk31(f,a1,b1,area1,error1,resabs,defab1)
        if(keyf.eq.4) call dqk41(f,a1,b1,area1,error1,resabs,defab1)
        if(keyf.eq.5) call dqk51(f,a1,b1,area1,error1,resabs,defab1)
        if(keyf.eq.6) call dqk61(f,a1,b1,area1,error1,resabs,defab1)
        if(keyf.eq.1) call dqk15(f,a2,b2,area2,error2,resabs,defab2)
        if(keyf.eq.2) call dqk21(f,a2,b2,area2,error2,resabs,defab2)
        if(keyf.eq.3) call dqk31(f,a2,b2,area2,error2,resabs,defab2)
        if(keyf.eq.4) call dqk41(f,a2,b2,area2,error2,resabs,defab2)
        if(keyf.eq.5) call dqk51(f,a2,b2,area2,error2,resabs,defab2)
        if(keyf.eq.6) call dqk61(f,a2,b2,area2,error2,resabs,defab2)
c
c           improve previous approximations to integral
c           and error and test for accuracy.
c
        neval = neval+1
        area12 = area1+area2
        erro12 = error1+error2
        errsum = errsum+erro12-errmax
        area = area+area12-rlist(maxerr)
        if(defab1.eq.error1.or.defab2.eq.error2) go to 5
        if(abs(rlist(maxerr)-area12).le.0.1d-04*abs(area12)
     *  .and.erro12.ge.0.99d+00*errmax) iroff1 = iroff1+1
        if(last.gt.10.and.erro12.gt.errmax) iroff2 = iroff2+1
    5   rlist(maxerr) = area1
        rlist(last) = area2
        errbnd = max(epsabs,epsrel*abs(area))
        if(errsum.le.errbnd) go to 8
c
c           test for roundoff error and eventually set error flag.
c
        if(iroff1.ge.6.or.iroff2.ge.20) ier = 2
c
c           set error flag in the case that the number of subintervals
c           equals limit.
c
        if(last.eq.limit) ier = 1
c
c           set error flag in the case of bad integrand behaviour
c           at a point of the integration range.
c
        if(max(abs(a1),abs(b2)).le.(0.1d+01+0.1d+03*
     *  epmach)*(abs(a2)+0.1d+04*uflow)) ier = 3
c
c           append the newly-created intervals to the list.
c
    8   if(error2.gt.error1) go to 10
        alist(last) = a2
        blist(maxerr) = b1
        blist(last) = b2
        elist(maxerr) = error1
        elist(last) = error2
        go to 20
   10   alist(maxerr) = a2
        alist(last) = a1
        blist(last) = b1
        rlist(maxerr) = area2
        rlist(last) = area1
        elist(maxerr) = error2
        elist(last) = error1
c
c           call subroutine dqpsrt to maintain the descending ordering
c           in the list of error estimates and select the subinterval
c           with the largest error estimate (to be bisected next).
c
   20   call dqpsrt(limit,last,maxerr,errmax,elist,iord,nrmax)
c ***jump out of do-loop
        if(ier.ne.0.or.errsum.le.errbnd) go to 40
   30 continue
c
c           compute final result.
c           ---------------------
c
   40 result = 0.0d+00
      do 50 k=1,last
        result = result+rlist(k)
   50 continue
      abserr = errsum
   60 if(keyf.ne.1) neval = (10*keyf+1)*(2*neval+1)
      if(keyf.eq.1) neval = 30*neval+15
  999 return
      end
      subroutine dqk15(f,a,b,result,abserr,resabs,resasc)
c***begin prologue  dqk15
c***date written   800101   (yymmdd)
c***revision date  830518   (yymmdd)
c***category no.  h2a1a2
c***keywords  15-point gauss-kronrod rules
c***author  piessens,robert,appl. math. & progr. div. - k.u.leuven
c           de doncker,elise,appl. math. & progr. div - k.u.leuven
c***purpose  to compute i = integral of f over (a,b), with error
c                           estimate
c                       j = integral of abs(f) over (a,b)
c***description
c
c           integration rules
c           standard fortran subroutine
c           real*8 version
c
c           parameters
c            on entry
c              f      - real*8
c                       function subprogram defining the integrand
c                       function f(x). the actual name for f needs to be
c                       declared e x t e r n a l in the calling program.
c
c              a      - real*8
c                       lower limit of integration
c
c              b      - real*8
c                       upper limit of integration
c
c            on return
c              result - real*8
c                       approximation to the integral i
c                       result is computed by applying the 15-point
c                       kronrod rule (resk) obtained by optimal addition
c                       of abscissae to the7-point gauss rule(resg).
c
c              abserr - real*8
c                       estimate of the modulus of the absolute error,
c                       which should not exceed abs(i-result)
c
c              resabs - real*8
c                       approximation to the integral j
c
c              resasc - real*8
c                       approximation to the integral of abs(f-i/(b-a))
c                       over (a,b)
c
c***references  (none)
c***routines called  d1mach
c***end prologue  dqk15
c
      real*8 a,absc,abserr,b,centr,dhlgth,
     *  d1mach,epmach,f,fc,fsum,fval1,fval2,fv1,fv2,hlgth,resabs,resasc,
     *  resg,resk,reskh,result,uflow,wg,wgk,xgk
      integer j,jtw,jtwm1
      external f
c
      dimension fv1(7),fv2(7),wg(4),wgk(8),xgk(8)
c
c           the abscissae and weights are given for the interval (-1,1).
c           because of symmetry only the positive abscissae and their
c           corresponding weights are given.
c
c           xgk    - abscissae of the 15-point kronrod rule
c                    xgk(2), xgk(4), ...  abscissae of the 7-point
c                    gauss rule
c                    xgk(1), xgk(3), ...  abscissae which are optimally
c                    added to the 7-point gauss rule
c
c           wgk    - weights of the 15-point kronrod rule
c
c           wg     - weights of the 7-point gauss rule
c
c
c gauss quadrature weights and kronron quadrature abscissae and weights
c as evaluated with 80 decimal digit arithmetic by l. w. fullerton,
c bell labs, nov. 1981.
c
      data wg  (  1) / 0.1294849661 6886969327 0611432679 082 d0 /
      data wg  (  2) / 0.2797053914 8927666790 1467771423 780 d0 /
      data wg  (  3) / 0.3818300505 0511894495 0369775488 975 d0 /
      data wg  (  4) / 0.4179591836 7346938775 5102040816 327 d0 /
c
      data xgk (  1) / 0.9914553711 2081263920 6854697526 329 d0 /
      data xgk (  2) / 0.9491079123 4275852452 6189684047 851 d0 /
      data xgk (  3) / 0.8648644233 5976907278 9712788640 926 d0 /
      data xgk (  4) / 0.7415311855 9939443986 3864773280 788 d0 /
      data xgk (  5) / 0.5860872354 6769113029 4144838258 730 d0 /
      data xgk (  6) / 0.4058451513 7739716690 6606412076 961 d0 /
      data xgk (  7) / 0.2077849550 0789846760 0689403773 245 d0 /
      data xgk (  8) / 0.0000000000 0000000000 0000000000 000 d0 /
c
      data wgk (  1) / 0.0229353220 1052922496 3732008058 970 d0 /
      data wgk (  2) / 0.0630920926 2997855329 0700663189 204 d0 /
      data wgk (  3) / 0.1047900103 2225018383 9876322541 518 d0 /
      data wgk (  4) / 0.1406532597 1552591874 5189590510 238 d0 /
      data wgk (  5) / 0.1690047266 3926790282 6583426598 550 d0 /
      data wgk (  6) / 0.1903505780 6478540991 3256402421 014 d0 /
      data wgk (  7) / 0.2044329400 7529889241 4161999234 649 d0 /
      data wgk (  8) / 0.2094821410 8472782801 2999174891 714 d0 /
c
c
c           list of major variables
c           -----------------------
c
c           centr  - mid point of the interval
c           hlgth  - half-length of the interval
c           absc   - abscissa
c           fval*  - function value
c           resg   - result of the 7-point gauss formula
c           resk   - result of the 15-point kronrod formula
c           reskh  - approximation to the mean value of f over (a,b),
c                    i.e. to i/(b-a)
c
c           machine dependent constants
c           ---------------------------
c
c           epmach is the largest relative spacing.
c           uflow is the smallest positive magnitude.
c
c***first executable statement  dqk15
      epmach = d1mach(4)
      uflow = d1mach(1)
c
      centr = 0.5d+00*(a+b)
      hlgth = 0.5d+00*(b-a)
      dhlgth = abs(hlgth)
c
c           compute the 15-point kronrod approximation to
c           the integral, and estimate the absolute error.
c
      fc = f(centr)
      resg = fc*wg(4)
      resk = fc*wgk(8)
      resabs = abs(resk)
      do 10 j=1,3
        jtw = j*2
        absc = hlgth*xgk(jtw)
        fval1 = f(centr-absc)
        fval2 = f(centr+absc)
        fv1(jtw) = fval1
        fv2(jtw) = fval2
        fsum = fval1+fval2
        resg = resg+wg(j)*fsum
        resk = resk+wgk(jtw)*fsum
        resabs = resabs+wgk(jtw)*(abs(fval1)+abs(fval2))
   10 continue
      do 15 j = 1,4
        jtwm1 = j*2-1
        absc = hlgth*xgk(jtwm1)
        fval1 = f(centr-absc)
        fval2 = f(centr+absc)
        fv1(jtwm1) = fval1
        fv2(jtwm1) = fval2
        fsum = fval1+fval2
        resk = resk+wgk(jtwm1)*fsum
        resabs = resabs+wgk(jtwm1)*(abs(fval1)+abs(fval2))
   15 continue
      reskh = resk*0.5d+00
      resasc = wgk(8)*abs(fc-reskh)
      do 20 j=1,7
        resasc = resasc+wgk(j)*(abs(fv1(j)-reskh)+abs(fv2(j)-reskh))
   20 continue
      result = resk*hlgth
      resabs = resabs*dhlgth
      resasc = resasc*dhlgth
      abserr = abs((resk-resg)*hlgth)
      if(resasc.ne.0.0d+00.and.abserr.ne.0.0d+00)
     *  abserr = resasc*min(0.1d+01,(0.2d+03*abserr/resasc)**1.5d+00)
      if(resabs.gt.uflow/(0.5d+02*epmach)) abserr = max
     *  ((epmach*0.5d+02)*resabs,abserr)
      return
      end
      subroutine dqk21(f,a,b,result,abserr,resabs,resasc)
c***begin prologue  dqk21
c***date written   800101   (yymmdd)
c***revision date  830518   (yymmdd)
c***category no.  h2a1a2
c***keywords  21-point gauss-kronrod rules
c***author  piessens,robert,appl. math. & progr. div. - k.u.leuven
c           de doncker,elise,appl. math. & progr. div. - k.u.leuven
c***purpose  to compute i = integral of f over (a,b), with error
c                           estimate
c                       j = integral of abs(f) over (a,b)
c***description
c
c           integration rules
c           standard fortran subroutine
c           real*8 version
c
c           parameters
c            on entry
c              f      - real*8
c                       function subprogram defining the integrand
c                       function f(x). the actual name for f needs to be
c                       declared e x t e r n a l in the driver program.
c
c              a      - real*8
c                       lower limit of integration
c
c              b      - real*8
c                       upper limit of integration
c
c            on return
c              result - real*8
c                       approximation to the integral i
c                       result is computed by applying the 21-point
c                       kronrod rule (resk) obtained by optimal addition
c                       of abscissae to the 10-point gauss rule (resg).
c
c              abserr - real*8
c                       estimate of the modulus of the absolute error,
c                       which should not exceed abs(i-result)
c
c              resabs - real*8
c                       approximation to the integral j
c
c              resasc - real*8
c                       approximation to the integral of abs(f-i/(b-a))
c                       over (a,b)
c
c***references  (none)
c***routines called  d1mach
c***end prologue  dqk21
c
      real*8 a,absc,abserr,b,centr,dhlgth,
     *  d1mach,epmach,f,fc,fsum,fval1,fval2,fv1,fv2,hlgth,resabs,resasc,
     *  resg,resk,reskh,result,uflow,wg,wgk,xgk
      integer j,jtw,jtwm1
      external f
c
      dimension fv1(10),fv2(10),wg(5),wgk(11),xgk(11)
c
c           the abscissae and weights are given for the interval (-1,1).
c           because of symmetry only the positive abscissae and their
c           corresponding weights are given.
c
c           xgk    - abscissae of the 21-point kronrod rule
c                    xgk(2), xgk(4), ...  abscissae of the 10-point
c                    gauss rule
c                    xgk(1), xgk(3), ...  abscissae which are optimally
c                    added to the 10-point gauss rule
c
c           wgk    - weights of the 21-point kronrod rule
c
c           wg     - weights of the 10-point gauss rule
c
c
c gauss quadrature weights and kronron quadrature abscissae and weights
c as evaluated with 80 decimal digit arithmetic by l. w. fullerton,
c bell labs, nov. 1981.
c
      data wg  (  1) / 0.0666713443 0868813759 3568809893 332 d0 /
      data wg  (  2) / 0.1494513491 5058059314 5776339657 697 d0 /
      data wg  (  3) / 0.2190863625 1598204399 5534934228 163 d0 /
      data wg  (  4) / 0.2692667193 0999635509 1226921569 469 d0 /
      data wg  (  5) / 0.2955242247 1475287017 3892994651 338 d0 /
c
      data xgk (  1) / 0.9956571630 2580808073 5527280689 003 d0 /
      data xgk (  2) / 0.9739065285 1717172007 7964012084 452 d0 /
      data xgk (  3) / 0.9301574913 5570822600 1207180059 508 d0 /
      data xgk (  4) / 0.8650633666 8898451073 2096688423 493 d0 /
      data xgk (  5) / 0.7808177265 8641689706 3717578345 042 d0 /
      data xgk (  6) / 0.6794095682 9902440623 4327365114 874 d0 /
      data xgk (  7) / 0.5627571346 6860468333 9000099272 694 d0 /
      data xgk (  8) / 0.4333953941 2924719079 9265943165 784 d0 /
      data xgk (  9) / 0.2943928627 0146019813 1126603103 866 d0 /
      data xgk ( 10) / 0.1488743389 8163121088 4826001129 720 d0 /
      data xgk ( 11) / 0.0000000000 0000000000 0000000000 000 d0 /
c
      data wgk (  1) / 0.0116946388 6737187427 8064396062 192 d0 /
      data wgk (  2) / 0.0325581623 0796472747 8818972459 390 d0 /
      data wgk (  3) / 0.0547558965 7435199603 1381300244 580 d0 /
      data wgk (  4) / 0.0750396748 1091995276 7043140916 190 d0 /
      data wgk (  5) / 0.0931254545 8369760553 5065465083 366 d0 /
      data wgk (  6) / 0.1093871588 0229764189 9210590325 805 d0 /
      data wgk (  7) / 0.1234919762 6206585107 7958109831 074 d0 /
      data wgk (  8) / 0.1347092173 1147332592 8054001771 707 d0 /
      data wgk (  9) / 0.1427759385 7706008079 7094273138 717 d0 /
      data wgk ( 10) / 0.1477391049 0133849137 4841515972 068 d0 /
      data wgk ( 11) / 0.1494455540 0291690566 4936468389 821 d0 /
c
c
c           list of major variables
c           -----------------------
c
c           centr  - mid point of the interval
c           hlgth  - half-length of the interval
c           absc   - abscissa
c           fval*  - function value
c           resg   - result of the 10-point gauss formula
c           resk   - result of the 21-point kronrod formula
c           reskh  - approximation to the mean value of f over (a,b),
c                    i.e. to i/(b-a)
c
c
c           machine dependent constants
c           ---------------------------
c
c           epmach is the largest relative spacing.
c           uflow is the smallest positive magnitude.
c
c***first executable statement  dqk21
      epmach = d1mach(4)
      uflow = d1mach(1)
c
      centr = 0.5d+00*(a+b)
      hlgth = 0.5d+00*(b-a)
      dhlgth = abs(hlgth)
c
c           compute the 21-point kronrod approximation to
c           the integral, and estimate the absolute error.
c
      resg = 0.0d+00
      fc = f(centr)
      resk = wgk(11)*fc
      resabs = abs(resk)
      do 10 j=1,5
        jtw = 2*j
        absc = hlgth*xgk(jtw)
        fval1 = f(centr-absc)
        fval2 = f(centr+absc)
        fv1(jtw) = fval1
        fv2(jtw) = fval2
        fsum = fval1+fval2
        resg = resg+wg(j)*fsum
        resk = resk+wgk(jtw)*fsum
        resabs = resabs+wgk(jtw)*(abs(fval1)+abs(fval2))
   10 continue
      do 15 j = 1,5
        jtwm1 = 2*j-1
        absc = hlgth*xgk(jtwm1)
        fval1 = f(centr-absc)
        fval2 = f(centr+absc)
        fv1(jtwm1) = fval1
        fv2(jtwm1) = fval2
        fsum = fval1+fval2
        resk = resk+wgk(jtwm1)*fsum
        resabs = resabs+wgk(jtwm1)*(abs(fval1)+abs(fval2))
   15 continue
      reskh = resk*0.5d+00
      resasc = wgk(11)*abs(fc-reskh)
      do 20 j=1,10
        resasc = resasc+wgk(j)*(abs(fv1(j)-reskh)+abs(fv2(j)-reskh))
   20 continue
      result = resk*hlgth
      resabs = resabs*dhlgth
      resasc = resasc*dhlgth
      abserr = abs((resk-resg)*hlgth)
      if(resasc.ne.0.0d+00.and.abserr.ne.0.0d+00)
     *  abserr = resasc*min(0.1d+01,(0.2d+03*abserr/resasc)**1.5d+00)
      if(resabs.gt.uflow/(0.5d+02*epmach)) abserr = max
     *  ((epmach*0.5d+02)*resabs,abserr)
      return
      end
      subroutine dqk31(f,a,b,result,abserr,resabs,resasc)
c***begin prologue  dqk31
c***date written   800101   (yymmdd)
c***revision date  830518   (yymmdd)
c***category no.  h2a1a2
c***keywords  31-point gauss-kronrod rules
c***author  piessens,robert,appl. math. & progr. div. - k.u.leuven
c           de doncker,elise,appl. math. & progr. div. - k.u.leuven
c***purpose  to compute i = integral of f over (a,b) with error
c                           estimate
c                       j = integral of abs(f) over (a,b)
c***description
c
c           integration rules
c           standard fortran subroutine
c           real*8 version
c
c           parameters
c            on entry
c              f      - real*8
c                       function subprogram defining the integrand
c                       function f(x). the actual name for f needs to be
c                       declared e x t e r n a l in the calling program.
c
c              a      - real*8
c                       lower limit of integration
c
c              b      - real*8
c                       upper limit of integration
c
c            on return
c              result - real*8
c                       approximation to the integral i
c                       result is computed by applying the 31-point
c                       gauss-kronrod rule (resk), obtained by optimal
c                       addition of abscissae to the 15-point gauss
c                       rule (resg).
c
c              abserr - double precison
c                       estimate of the modulus of the modulus,
c                       which should not exceed abs(i-result)
c
c              resabs - real*8
c                       approximation to the integral j
c
c              resasc - real*8
c                       approximation to the integral of abs(f-i/(b-a))
c                       over (a,b)
c
c***references  (none)
c***routines called  d1mach
c***end prologue  dqk31
      real*8 a,absc,abserr,b,centr,dhlgth,
     *  d1mach,epmach,f,fc,fsum,fval1,fval2,fv1,fv2,hlgth,resabs,resasc,
     *  resg,resk,reskh,result,uflow,wg,wgk,xgk
      integer j,jtw,jtwm1
      external f
c
      dimension fv1(15),fv2(15),xgk(16),wgk(16),wg(8)
c
c           the abscissae and weights are given for the interval (-1,1).
c           because of symmetry only the positive abscissae and their
c           corresponding weights are given.
c
c           xgk    - abscissae of the 31-point kronrod rule
c                    xgk(2), xgk(4), ...  abscissae of the 15-point
c                    gauss rule
c                    xgk(1), xgk(3), ...  abscissae which are optimally
c                    added to the 15-point gauss rule
c
c           wgk    - weights of the 31-point kronrod rule
c
c           wg     - weights of the 15-point gauss rule
c
c
c gauss quadrature weights and kronron quadrature abscissae and weights
c as evaluated with 80 decimal digit arithmetic by l. w. fullerton,
c bell labs, nov. 1981.
c
      data wg  (  1) / 0.0307532419 9611726835 4628393577 204 d0 /
      data wg  (  2) / 0.0703660474 8810812470 9267416450 667 d0 /
      data wg  (  3) / 0.1071592204 6717193501 1869546685 869 d0 /
      data wg  (  4) / 0.1395706779 2615431444 7804794511 028 d0 /
      data wg  (  5) / 0.1662692058 1699393355 3200860481 209 d0 /
      data wg  (  6) / 0.1861610000 1556221102 6800561866 423 d0 /
      data wg  (  7) / 0.1984314853 2711157645 6118326443 839 d0 /
      data wg  (  8) / 0.2025782419 2556127288 0620199967 519 d0 /
c
      data xgk (  1) / 0.9980022986 9339706028 5172840152 271 d0 /
      data xgk (  2) / 0.9879925180 2048542848 9565718586 613 d0 /
      data xgk (  3) / 0.9677390756 7913913425 7347978784 337 d0 /
      data xgk (  4) / 0.9372733924 0070590430 7758947710 209 d0 /
      data xgk (  5) / 0.8972645323 4408190088 2509656454 496 d0 /
      data xgk (  6) / 0.8482065834 1042721620 0648320774 217 d0 /
      data xgk (  7) / 0.7904185014 4246593296 7649294817 947 d0 /
      data xgk (  8) / 0.7244177313 6017004741 6186054613 938 d0 /
      data xgk (  9) / 0.6509967412 9741697053 3735895313 275 d0 /
      data xgk ( 10) / 0.5709721726 0853884753 7226737253 911 d0 /
      data xgk ( 11) / 0.4850818636 4023968069 3655740232 351 d0 /
      data xgk ( 12) / 0.3941513470 7756336989 7207370981 045 d0 /
      data xgk ( 13) / 0.2991800071 5316881216 6780024266 389 d0 /
      data xgk ( 14) / 0.2011940939 9743452230 0628303394 596 d0 /
      data xgk ( 15) / 0.1011420669 1871749902 7074231447 392 d0 /
      data xgk ( 16) / 0.0000000000 0000000000 0000000000 000 d0 /
c
      data wgk (  1) / 0.0053774798 7292334898 7792051430 128 d0 /
      data wgk (  2) / 0.0150079473 2931612253 8374763075 807 d0 /
      data wgk (  3) / 0.0254608473 2671532018 6874001019 653 d0 /
      data wgk (  4) / 0.0353463607 9137584622 2037948478 360 d0 /
      data wgk (  5) / 0.0445897513 2476487660 8227299373 280 d0 /
      data wgk (  6) / 0.0534815246 9092808726 5343147239 430 d0 /
      data wgk (  7) / 0.0620095678 0067064028 5139230960 803 d0 /
      data wgk (  8) / 0.0698541213 1872825870 9520077099 147 d0 /
      data wgk (  9) / 0.0768496807 5772037889 4432777482 659 d0 /
      data wgk ( 10) / 0.0830805028 2313302103 8289247286 104 d0 /
      data wgk ( 11) / 0.0885644430 5621177064 7275443693 774 d0 /
      data wgk ( 12) / 0.0931265981 7082532122 5486872747 346 d0 /
      data wgk ( 13) / 0.0966427269 8362367850 5179907627 589 d0 /
      data wgk ( 14) / 0.0991735987 2179195933 2393173484 603 d0 /
      data wgk ( 15) / 0.1007698455 2387559504 4946662617 570 d0 /
      data wgk ( 16) / 0.1013300070 1479154901 7374792767 493 d0 /
c
c
c           list of major variables
c           -----------------------
c           centr  - mid point of the interval
c           hlgth  - half-length of the interval
c           absc   - abscissa
c           fval*  - function value
c           resg   - result of the 15-point gauss formula
c           resk   - result of the 31-point kronrod formula
c           reskh  - approximation to the mean value of f over (a,b),
c                    i.e. to i/(b-a)
c
c           machine dependent constants
c           ---------------------------
c           epmach is the largest relative spacing.
c           uflow is the smallest positive magnitude.
c***first executable statement  dqk31
      epmach = d1mach(4)
      uflow = d1mach(1)
c
      centr = 0.5d+00*(a+b)
      hlgth = 0.5d+00*(b-a)
      dhlgth = abs(hlgth)
c
c           compute the 31-point kronrod approximation to
c           the integral, and estimate the absolute error.
c
      fc = f(centr)
      resg = wg(8)*fc
      resk = wgk(16)*fc
      resabs = abs(resk)
      do 10 j=1,7
        jtw = j*2
        absc = hlgth*xgk(jtw)
        fval1 = f(centr-absc)
        fval2 = f(centr+absc)
        fv1(jtw) = fval1
        fv2(jtw) = fval2
        fsum = fval1+fval2
        resg = resg+wg(j)*fsum
        resk = resk+wgk(jtw)*fsum
        resabs = resabs+wgk(jtw)*(abs(fval1)+abs(fval2))
   10 continue
      do 15 j = 1,8
        jtwm1 = j*2-1
        absc = hlgth*xgk(jtwm1)
        fval1 = f(centr-absc)
        fval2 = f(centr+absc)
        fv1(jtwm1) = fval1
        fv2(jtwm1) = fval2
        fsum = fval1+fval2
        resk = resk+wgk(jtwm1)*fsum
        resabs = resabs+wgk(jtwm1)*(abs(fval1)+abs(fval2))
   15 continue
      reskh = resk*0.5d+00
      resasc = wgk(16)*abs(fc-reskh)
      do 20 j=1,15
        resasc = resasc+wgk(j)*(abs(fv1(j)-reskh)+abs(fv2(j)-reskh))
   20 continue
      result = resk*hlgth
      resabs = resabs*dhlgth
      resasc = resasc*dhlgth
      abserr = abs((resk-resg)*hlgth)
      if(resasc.ne.0.0d+00.and.abserr.ne.0.0d+00)
     *  abserr = resasc*min(0.1d+01,(0.2d+03*abserr/resasc)**1.5d+00)
      if(resabs.gt.uflow/(0.5d+02*epmach)) abserr = max
     *  ((epmach*0.5d+02)*resabs,abserr)
      return
      end
      subroutine dqk41(f,a,b,result,abserr,resabs,resasc)
c***begin prologue  dqk41
c***date written   800101   (yymmdd)
c***revision date  830518   (yymmdd)
c***category no.  h2a1a2
c***keywords  41-point gauss-kronrod rules
c***author  piessens,robert,appl. math. & progr. div. - k.u.leuven
c           de doncker,elise,appl. math. & progr. div. - k.u.leuven
c***purpose  to compute i = integral of f over (a,b), with error
c                           estimate
c                       j = integral of abs(f) over (a,b)
c***description
c
c           integration rules
c           standard fortran subroutine
c           real*8 version
c
c           parameters
c            on entry
c              f      - real*8
c                       function subprogram defining the integrand
c                       function f(x). the actual name for f needs to be
c                       declared e x t e r n a l in the calling program.
c
c              a      - real*8
c                       lower limit of integration
c
c              b      - real*8
c                       upper limit of integration
c
c            on return
c              result - real*8
c                       approximation to the integral i
c                       result is computed by applying the 41-point
c                       gauss-kronrod rule (resk) obtained by optimal
c                       addition of abscissae to the 20-point gauss
c                       rule (resg).
c
c              abserr - real*8
c                       estimate of the modulus of the absolute error,
c                       which should not exceed abs(i-result)
c
c              resabs - real*8
c                       approximation to the integral j
c
c              resasc - real*8
c                       approximation to the integal of abs(f-i/(b-a))
c                       over (a,b)
c
c***references  (none)
c***routines called  d1mach
c***end prologue  dqk41
c
      real*8 a,absc,abserr,b,centr,dhlgth,
     *  d1mach,epmach,f,fc,fsum,fval1,fval2,fv1,fv2,hlgth,resabs,resasc,
     *  resg,resk,reskh,result,uflow,wg,wgk,xgk
      integer j,jtw,jtwm1
      external f
c
      dimension fv1(20),fv2(20),xgk(21),wgk(21),wg(10)
c
c           the abscissae and weights are given for the interval (-1,1).
c           because of symmetry only the positive abscissae and their
c           corresponding weights are given.
c
c           xgk    - abscissae of the 41-point gauss-kronrod rule
c                    xgk(2), xgk(4), ...  abscissae of the 20-point
c                    gauss rule
c                    xgk(1), xgk(3), ...  abscissae which are optimally
c                    added to the 20-point gauss rule
c
c           wgk    - weights of the 41-point gauss-kronrod rule
c
c           wg     - weights of the 20-point gauss rule
c
c
c gauss quadrature weights and kronron quadrature abscissae and weights
c as evaluated with 80 decimal digit arithmetic by l. w. fullerton,
c bell labs, nov. 1981.
c
      data wg  (  1) / 0.0176140071 3915211831 1861962351 853 d0 /
      data wg  (  2) / 0.0406014298 0038694133 1039952274 932 d0 /
      data wg  (  3) / 0.0626720483 3410906356 9506535187 042 d0 /
      data wg  (  4) / 0.0832767415 7670474872 4758143222 046 d0 /
      data wg  (  5) / 0.1019301198 1724043503 6750135480 350 d0 /
      data wg  (  6) / 0.1181945319 6151841731 2377377711 382 d0 /
      data wg  (  7) / 0.1316886384 4917662689 8494499748 163 d0 /
      data wg  (  8) / 0.1420961093 1838205132 9298325067 165 d0 /
      data wg  (  9) / 0.1491729864 7260374678 7828737001 969 d0 /
      data wg  ( 10) / 0.1527533871 3072585069 8084331955 098 d0 /
c
      data xgk (  1) / 0.9988590315 8827766383 8315576545 863 d0 /
      data xgk (  2) / 0.9931285991 8509492478 6122388471 320 d0 /
      data xgk (  3) / 0.9815078774 5025025919 3342994720 217 d0 /
      data xgk (  4) / 0.9639719272 7791379126 7666131197 277 d0 /
      data xgk (  5) / 0.9408226338 3175475351 9982722212 443 d0 /
      data xgk (  6) / 0.9122344282 5132590586 7752441203 298 d0 /
      data xgk (  7) / 0.8782768112 5228197607 7442995113 078 d0 /
      data xgk (  8) / 0.8391169718 2221882339 4529061701 521 d0 /
      data xgk (  9) / 0.7950414288 3755119835 0638833272 788 d0 /
      data xgk ( 10) / 0.7463319064 6015079261 4305070355 642 d0 /
      data xgk ( 11) / 0.6932376563 3475138480 5490711845 932 d0 /
      data xgk ( 12) / 0.6360536807 2651502545 2836696226 286 d0 /
      data xgk ( 13) / 0.5751404468 1971031534 2946036586 425 d0 /
      data xgk ( 14) / 0.5108670019 5082709800 4364050955 251 d0 /
      data xgk ( 15) / 0.4435931752 3872510319 9992213492 640 d0 /
      data xgk ( 16) / 0.3737060887 1541956067 2548177024 927 d0 /
      data xgk ( 17) / 0.3016278681 1491300432 0555356858 592 d0 /
      data xgk ( 18) / 0.2277858511 4164507808 0496195368 575 d0 /
      data xgk ( 19) / 0.1526054652 4092267550 5220241022 678 d0 /
      data xgk ( 20) / 0.0765265211 3349733375 4640409398 838 d0 /
      data xgk ( 21) / 0.0000000000 0000000000 0000000000 000 d0 /
c
      data wgk (  1) / 0.0030735837 1852053150 1218293246 031 d0 /
      data wgk (  2) / 0.0086002698 5564294219 8661787950 102 d0 /
      data wgk (  3) / 0.0146261692 5697125298 3787960308 868 d0 /
      data wgk (  4) / 0.0203883734 6126652359 8010231432 755 d0 /
      data wgk (  5) / 0.0258821336 0495115883 4505067096 153 d0 /
      data wgk (  6) / 0.0312873067 7703279895 8543119323 801 d0 /
      data wgk (  7) / 0.0366001697 5820079803 0557240707 211 d0 /
      data wgk (  8) / 0.0416688733 2797368626 3788305936 895 d0 /
      data wgk (  9) / 0.0464348218 6749767472 0231880926 108 d0 /
      data wgk ( 10) / 0.0509445739 2372869193 2707670050 345 d0 /
      data wgk ( 11) / 0.0551951053 4828599474 4832372419 777 d0 /
      data wgk ( 12) / 0.0591114008 8063957237 4967220648 594 d0 /
      data wgk ( 13) / 0.0626532375 5478116802 5870122174 255 d0 /
      data wgk ( 14) / 0.0658345971 3361842211 1563556969 398 d0 /
      data wgk ( 15) / 0.0686486729 2852161934 5623411885 368 d0 /
      data wgk ( 16) / 0.0710544235 5344406830 5790361723 210 d0 /
      data wgk ( 17) / 0.0730306903 3278666749 5189417658 913 d0 /
      data wgk ( 18) / 0.0745828754 0049918898 6581418362 488 d0 /
      data wgk ( 19) / 0.0757044976 8455667465 9542775376 617 d0 /
      data wgk ( 20) / 0.0763778676 7208073670 5502835038 061 d0 /
      data wgk ( 21) / 0.0766007119 1799965644 5049901530 102 d0 /
c
c
c           list of major variables
c           -----------------------
c
c           centr  - mid point of the interval
c           hlgth  - half-length of the interval
c           absc   - abscissa
c           fval*  - function value
c           resg   - result of the 20-point gauss formula
c           resk   - result of the 41-point kronrod formula
c           reskh  - approximation to mean value of f over (a,b), i.e.
c                    to i/(b-a)
c
c           machine dependent constants
c           ---------------------------
c
c           epmach is the largest relative spacing.
c           uflow is the smallest positive magnitude.
c
c***first executable statement  dqk41
      epmach = d1mach(4)
      uflow = d1mach(1)
c
      centr = 0.5d+00*(a+b)
      hlgth = 0.5d+00*(b-a)
      dhlgth = abs(hlgth)
c
c           compute the 41-point gauss-kronrod approximation to
c           the integral, and estimate the absolute error.
c
      resg = 0.0d+00
      fc = f(centr)
      resk = wgk(21)*fc
      resabs = abs(resk)
      do 10 j=1,10
        jtw = j*2
        absc = hlgth*xgk(jtw)
        fval1 = f(centr-absc)
        fval2 = f(centr+absc)
        fv1(jtw) = fval1
        fv2(jtw) = fval2
        fsum = fval1+fval2
        resg = resg+wg(j)*fsum
        resk = resk+wgk(jtw)*fsum
        resabs = resabs+wgk(jtw)*(abs(fval1)+abs(fval2))
   10 continue
      do 15 j = 1,10
        jtwm1 = j*2-1
        absc = hlgth*xgk(jtwm1)
        fval1 = f(centr-absc)
        fval2 = f(centr+absc)
        fv1(jtwm1) = fval1
        fv2(jtwm1) = fval2
        fsum = fval1+fval2
        resk = resk+wgk(jtwm1)*fsum
        resabs = resabs+wgk(jtwm1)*(abs(fval1)+abs(fval2))
   15 continue
      reskh = resk*0.5d+00
      resasc = wgk(21)*abs(fc-reskh)
      do 20 j=1,20
        resasc = resasc+wgk(j)*(abs(fv1(j)-reskh)+abs(fv2(j)-reskh))
   20 continue
      result = resk*hlgth
      resabs = resabs*dhlgth
      resasc = resasc*dhlgth
      abserr = abs((resk-resg)*hlgth)
      if(resasc.ne.0.0d+00.and.abserr.ne.0.d+00)
     *  abserr = resasc*min(0.1d+01,(0.2d+03*abserr/resasc)**1.5d+00)
      if(resabs.gt.uflow/(0.5d+02*epmach)) abserr = max
     *  ((epmach*0.5d+02)*resabs,abserr)
      return
      end
      subroutine dqk51(f,a,b,result,abserr,resabs,resasc)
c***begin prologue  dqk51
c***date written   800101   (yymmdd)
c***revision date  830518   (yymmdd)
c***category no.  h2a1a2
c***keywords  51-point gauss-kronrod rules
c***author  piessens,robert,appl. math. & progr. div. - k.u.leuven
c           de doncker,elise,appl. math & progr. div. - k.u.leuven
c***purpose  to compute i = integral of f over (a,b) with error
c                           estimate
c                       j = integral of abs(f) over (a,b)
c***description
c
c           integration rules
c           standard fortran subroutine
c           real*8 version
c
c           parameters
c            on entry
c              f      - real*8
c                       function subroutine defining the integrand
c                       function f(x). the actual name for f needs to be
c                       declared e x t e r n a l in the calling program.
c
c              a      - real*8
c                       lower limit of integration
c
c              b      - real*8
c                       upper limit of integration
c
c            on return
c              result - real*8
c                       approximation to the integral i
c                       result is computed by applying the 51-point
c                       kronrod rule (resk) obtained by optimal addition
c                       of abscissae to the 25-point gauss rule (resg).
c
c              abserr - real*8
c                       estimate of the modulus of the absolute error,
c                       which should not exceed abs(i-result)
c
c              resabs - real*8
c                       approximation to the integral j
c
c              resasc - real*8
c                       approximation to the integral of abs(f-i/(b-a))
c                       over (a,b)
c
c***references  (none)
c***routines called  d1mach
c***end prologue  dqk51
c
      real*8 a,absc,abserr,b,centr,dhlgth,
     *  d1mach,epmach,f,fc,fsum,fval1,fval2,fv1,fv2,hlgth,resabs,resasc,
     *  resg,resk,reskh,result,uflow,wg,wgk,xgk
      integer j,jtw,jtwm1
      external f
c
      dimension fv1(25),fv2(25),xgk(26),wgk(26),wg(13)
c
c           the abscissae and weights are given for the interval (-1,1).
c           because of symmetry only the positive abscissae and their
c           corresponding weights are given.
c
c           xgk    - abscissae of the 51-point kronrod rule
c                    xgk(2), xgk(4), ...  abscissae of the 25-point
c                    gauss rule
c                    xgk(1), xgk(3), ...  abscissae which are optimally
c                    added to the 25-point gauss rule
c
c           wgk    - weights of the 51-point kronrod rule
c
c           wg     - weights of the 25-point gauss rule
c
c
c gauss quadrature weights and kronron quadrature abscissae and weights
c as evaluated with 80 decimal digit arithmetic by l. w. fullerton,
c bell labs, nov. 1981.
c
      data wg  (  1) / 0.0113937985 0102628794 7902964113 235 d0 /
      data wg  (  2) / 0.0263549866 1503213726 1901815295 299 d0 /
      data wg  (  3) / 0.0409391567 0130631265 5623487711 646 d0 /
      data wg  (  4) / 0.0549046959 7583519192 5936891540 473 d0 /
      data wg  (  5) / 0.0680383338 1235691720 7187185656 708 d0 /
      data wg  (  6) / 0.0801407003 3500101801 3234959669 111 d0 /
      data wg  (  7) / 0.0910282619 8296364981 1497220702 892 d0 /
      data wg  (  8) / 0.1005359490 6705064420 2206890392 686 d0 /
      data wg  (  9) / 0.1085196244 7426365311 6093957050 117 d0 /
      data wg  ( 10) / 0.1148582591 4571164833 9325545869 556 d0 /
      data wg  ( 11) / 0.1194557635 3578477222 8178126512 901 d0 /
      data wg  ( 12) / 0.1222424429 9031004168 8959518945 852 d0 /
      data wg  ( 13) / 0.1231760537 2671545120 3902873079 050 d0 /
c
      data xgk (  1) / 0.9992621049 9260983419 3457486540 341 d0 /
      data xgk (  2) / 0.9955569697 9049809790 8784946893 902 d0 /
      data xgk (  3) / 0.9880357945 3407724763 7331014577 406 d0 /
      data xgk (  4) / 0.9766639214 5951751149 8315386479 594 d0 /
      data xgk (  5) / 0.9616149864 2584251241 8130033660 167 d0 /
      data xgk (  6) / 0.9429745712 2897433941 4011169658 471 d0 /
      data xgk (  7) / 0.9207471152 8170156174 6346084546 331 d0 /
      data xgk (  8) / 0.8949919978 7827536885 1042006782 805 d0 /
      data xgk (  9) / 0.8658470652 9327559544 8996969588 340 d0 /
      data xgk ( 10) / 0.8334426287 6083400142 1021108693 570 d0 /
      data xgk ( 11) / 0.7978737979 9850005941 0410904994 307 d0 /
      data xgk ( 12) / 0.7592592630 3735763057 7282865204 361 d0 /
      data xgk ( 13) / 0.7177664068 1308438818 6654079773 298 d0 /
      data xgk ( 14) / 0.6735663684 7346836448 5120633247 622 d0 /
      data xgk ( 15) / 0.6268100990 1031741278 8122681624 518 d0 /
      data xgk ( 16) / 0.5776629302 4122296772 3689841612 654 d0 /
      data xgk ( 17) / 0.5263252843 3471918259 9623778158 010 d0 /
      data xgk ( 18) / 0.4730027314 4571496052 2182115009 192 d0 /
      data xgk ( 19) / 0.4178853821 9303774885 1814394594 572 d0 /
      data xgk ( 20) / 0.3611723058 0938783773 5821730127 641 d0 /
      data xgk ( 21) / 0.3030895389 3110783016 7478909980 339 d0 /
      data xgk ( 22) / 0.2438668837 2098843204 5190362797 452 d0 /
      data xgk ( 23) / 0.1837189394 2104889201 5969888759 528 d0 /
      data xgk ( 24) / 0.1228646926 1071039638 7359818808 037 d0 /
      data xgk ( 25) / 0.0615444830 0568507888 6546392366 797 d0 /
      data xgk ( 26) / 0.0000000000 0000000000 0000000000 000 d0 /
c
      data wgk (  1) / 0.0019873838 9233031592 6507851882 843 d0 /
      data wgk (  2) / 0.0055619321 3535671375 8040236901 066 d0 /
      data wgk (  3) / 0.0094739733 8617415160 7207710523 655 d0 /
      data wgk (  4) / 0.0132362291 9557167481 3656405846 976 d0 /
      data wgk (  5) / 0.0168478177 0912829823 1516667536 336 d0 /
      data wgk (  6) / 0.0204353711 4588283545 6568292235 939 d0 /
      data wgk (  7) / 0.0240099456 0695321622 0092489164 881 d0 /
      data wgk (  8) / 0.0274753175 8785173780 2948455517 811 d0 /
      data wgk (  9) / 0.0307923001 6738748889 1109020215 229 d0 /
      data wgk ( 10) / 0.0340021302 7432933783 6748795229 551 d0 /
      data wgk ( 11) / 0.0371162714 8341554356 0330625367 620 d0 /
      data wgk ( 12) / 0.0400838255 0403238207 4839284467 076 d0 /
      data wgk ( 13) / 0.0428728450 2017004947 6895792439 495 d0 /
      data wgk ( 14) / 0.0455029130 4992178890 9870584752 660 d0 /
      data wgk ( 15) / 0.0479825371 3883671390 6392255756 915 d0 /
      data wgk ( 16) / 0.0502776790 8071567196 3325259433 440 d0 /
      data wgk ( 17) / 0.0523628858 0640747586 4366712137 873 d0 /
      data wgk ( 18) / 0.0542511298 8854549014 4543370459 876 d0 /
      data wgk ( 19) / 0.0559508112 2041231730 8240686382 747 d0 /
      data wgk ( 20) / 0.0574371163 6156783285 3582693939 506 d0 /
      data wgk ( 21) / 0.0586896800 2239420796 1974175856 788 d0 /
      data wgk ( 22) / 0.0597203403 2417405997 9099291932 562 d0 /
      data wgk ( 23) / 0.0605394553 7604586294 5360267517 565 d0 /
      data wgk ( 24) / 0.0611285097 1705304830 5859030416 293 d0 /
      data wgk ( 25) / 0.0614711898 7142531666 1544131965 264 d0 /
c       note: wgk (26) was calculated from the values of wgk(1..25)
      data wgk ( 26) / 0.0615808180 6783293507 8759824240 066 d0 /
c
c
c           list of major variables
c           -----------------------
c
c           centr  - mid point of the interval
c           hlgth  - half-length of the interval
c           absc   - abscissa
c           fval*  - function value
c           resg   - result of the 25-point gauss formula
c           resk   - result of the 51-point kronrod formula
c           reskh  - approximation to the mean value of f over (a,b),
c                    i.e. to i/(b-a)
c
c           machine dependent constants
c           ---------------------------
c
c           epmach is the largest relative spacing.
c           uflow is the smallest positive magnitude.
c
c***first executable statement  dqk51
      epmach = d1mach(4)
      uflow = d1mach(1)
c
      centr = 0.5d+00*(a+b)
      hlgth = 0.5d+00*(b-a)
      dhlgth = abs(hlgth)
c
c           compute the 51-point kronrod approximation to
c           the integral, and estimate the absolute error.
c
      fc = f(centr)
      resg = wg(13)*fc
      resk = wgk(26)*fc
      resabs = abs(resk)
      do 10 j=1,12
        jtw = j*2
        absc = hlgth*xgk(jtw)
        fval1 = f(centr-absc)
        fval2 = f(centr+absc)
        fv1(jtw) = fval1
        fv2(jtw) = fval2
        fsum = fval1+fval2
        resg = resg+wg(j)*fsum
        resk = resk+wgk(jtw)*fsum
        resabs = resabs+wgk(jtw)*(abs(fval1)+abs(fval2))
   10 continue
      do 15 j = 1,13
        jtwm1 = j*2-1
        absc = hlgth*xgk(jtwm1)
        fval1 = f(centr-absc)
        fval2 = f(centr+absc)
        fv1(jtwm1) = fval1
        fv2(jtwm1) = fval2
        fsum = fval1+fval2
        resk = resk+wgk(jtwm1)*fsum
        resabs = resabs+wgk(jtwm1)*(abs(fval1)+abs(fval2))
   15 continue
      reskh = resk*0.5d+00
      resasc = wgk(26)*abs(fc-reskh)
      do 20 j=1,25
        resasc = resasc+wgk(j)*(abs(fv1(j)-reskh)+abs(fv2(j)-reskh))
   20 continue
      result = resk*hlgth
      resabs = resabs*dhlgth
      resasc = resasc*dhlgth
      abserr = abs((resk-resg)*hlgth)
      if(resasc.ne.0.0d+00.and.abserr.ne.0.0d+00)
     *  abserr = resasc*min(0.1d+01,(0.2d+03*abserr/resasc)**1.5d+00)
      if(resabs.gt.uflow/(0.5d+02*epmach)) abserr = max
     *  ((epmach*0.5d+02)*resabs,abserr)
      return
      end
      subroutine dqk61(f,a,b,result,abserr,resabs,resasc)
c***begin prologue  dqk61
c***date written   800101   (yymmdd)
c***revision date  830518   (yymmdd)
c***category no.  h2a1a2
c***keywords  61-point gauss-kronrod rules
c***author  piessens,robert,appl. math. & progr. div. - k.u.leuven
c           de doncker,elise,appl. math. & progr. div. - k.u.leuven
c***purpose  to compute i = integral of f over (a,b) with error
c                           estimate
c                       j = integral of abs(f) over (a,b)
c***description
c
c        integration rule
c        standard fortran subroutine
c        real*8 version
c
c
c        parameters
c         on entry
c           f      - real*8
c                    function subprogram defining the integrand
c                    function f(x). the actual name for f needs to be
c                    declared e x t e r n a l in the calling program.
c
c           a      - real*8
c                    lower limit of integration
c
c           b      - real*8
c                    upper limit of integration
c
c         on return
c           result - real*8
c                    approximation to the integral i
c                    result is computed by applying the 61-point
c                    kronrod rule (resk) obtained by optimal addition of
c                    abscissae to the 30-point gauss rule (resg).
c
c           abserr - real*8
c                    estimate of the modulus of the absolute error,
c                    which should equal or exceed abs(i-result)
c
c           resabs - real*8
c                    approximation to the integral j
c
c           resasc - real*8
c                    approximation to the integral of abs(f-i/(b-a))
c
c
c***references  (none)
c***routines called  d1mach
c***end prologue  dqk61
c
      real*8 a,dabsc,abserr,b,centr,dhlgth,
     *  d1mach,epmach,f,fc,fsum,fval1,fval2,fv1,fv2,hlgth,resabs,resasc,
     *  resg,resk,reskh,result,uflow,wg,wgk,xgk
      integer j,jtw,jtwm1
      external f
c
      dimension fv1(30),fv2(30),xgk(31),wgk(31),wg(15)
c
c           the abscissae and weights are given for the
c           interval (-1,1). because of symmetry only the positive
c           abscissae and their corresponding weights are given.
c
c           xgk   - abscissae of the 61-point kronrod rule
c                   xgk(2), xgk(4)  ... abscissae of the 30-point
c                   gauss rule
c                   xgk(1), xgk(3)  ... optimally added abscissae
c                   to the 30-point gauss rule
c
c           wgk   - weights of the 61-point kronrod rule
c
c           wg    - weigths of the 30-point gauss rule
c
c
c gauss quadrature weights and kronron quadrature abscissae and weights
c as evaluated with 80 decimal digit arithmetic by l. w. fullerton,
c bell labs, nov. 1981.
c
      data wg  (  1) / 0.0079681924 9616660561 5465883474 674 d0 /
      data wg  (  2) / 0.0184664683 1109095914 2302131912 047 d0 /
      data wg  (  3) / 0.0287847078 8332336934 9719179611 292 d0 /
      data wg  (  4) / 0.0387991925 6962704959 6801936446 348 d0 /
      data wg  (  5) / 0.0484026728 3059405290 2938140422 808 d0 /
      data wg  (  6) / 0.0574931562 1761906648 1721689402 056 d0 /
      data wg  (  7) / 0.0659742298 8218049512 8128515115 962 d0 /
      data wg  (  8) / 0.0737559747 3770520626 8243850022 191 d0 /
      data wg  (  9) / 0.0807558952 2942021535 4694938460 530 d0 /
      data wg  ( 10) / 0.0868997872 0108297980 2387530715 126 d0 /
      data wg  ( 11) / 0.0921225222 3778612871 7632707087 619 d0 /
      data wg  ( 12) / 0.0963687371 7464425963 9468626351 810 d0 /
      data wg  ( 13) / 0.0995934205 8679526706 2780282103 569 d0 /
      data wg  ( 14) / 0.1017623897 4840550459 6428952168 554 d0 /
      data wg  ( 15) / 0.1028526528 9355884034 1285636705 415 d0 /
c
      data xgk (  1) / 0.9994844100 5049063757 1325895705 811 d0 /
      data xgk (  2) / 0.9968934840 7464954027 1630050918 695 d0 /
      data xgk (  3) / 0.9916309968 7040459485 8628366109 486 d0 /
      data xgk (  4) / 0.9836681232 7974720997 0032581605 663 d0 /
      data xgk (  5) / 0.9731163225 0112626837 4693868423 707 d0 /
      data xgk (  6) / 0.9600218649 6830751221 6871025581 798 d0 /
      data xgk (  7) / 0.9443744447 4855997941 5831324037 439 d0 /
      data xgk (  8) / 0.9262000474 2927432587 9324277080 474 d0 /
      data xgk (  9) / 0.9055733076 9990779854 6522558925 958 d0 /
      data xgk ( 10) / 0.8825605357 9205268154 3116462530 226 d0 /
      data xgk ( 11) / 0.8572052335 4606109895 8658510658 944 d0 /
      data xgk ( 12) / 0.8295657623 8276839744 2898119732 502 d0 /
      data xgk ( 13) / 0.7997278358 2183908301 3668942322 683 d0 /
      data xgk ( 14) / 0.7677774321 0482619491 7977340974 503 d0 /
      data xgk ( 15) / 0.7337900624 5322680472 6171131369 528 d0 /
      data xgk ( 16) / 0.6978504947 9331579693 2292388026 640 d0 /
      data xgk ( 17) / 0.6600610641 2662696137 0053668149 271 d0 /
      data xgk ( 18) / 0.6205261829 8924286114 0477556431 189 d0 /
      data xgk ( 19) / 0.5793452358 2636169175 6024932172 540 d0 /
      data xgk ( 20) / 0.5366241481 4201989926 4169793311 073 d0 /
      data xgk ( 21) / 0.4924804678 6177857499 3693061207 709 d0 /
      data xgk ( 22) / 0.4470337695 3808917678 0609900322 854 d0 /
      data xgk ( 23) / 0.4004012548 3039439253 5476211542 661 d0 /
      data xgk ( 24) / 0.3527047255 3087811347 1037207089 374 d0 /
      data xgk ( 25) / 0.3040732022 7362507737 2677107199 257 d0 /
      data xgk ( 26) / 0.2546369261 6788984643 9805129817 805 d0 /
      data xgk ( 27) / 0.2045251166 8230989143 8957671002 025 d0 /
      data xgk ( 28) / 0.1538699136 0858354696 3794672743 256 d0 /
      data xgk ( 29) / 0.1028069379 6673703014 7096751318 001 d0 /
      data xgk ( 30) / 0.0514718425 5531769583 3025213166 723 d0 /
      data xgk ( 31) / 0.0000000000 0000000000 0000000000 000 d0 /
c
      data wgk (  1) / 0.0013890136 9867700762 4551591226 760 d0 /
      data wgk (  2) / 0.0038904611 2709988405 1267201844 516 d0 /
      data wgk (  3) / 0.0066307039 1593129217 3319826369 750 d0 /
      data wgk (  4) / 0.0092732796 5951776342 8441146892 024 d0 /
      data wgk (  5) / 0.0118230152 5349634174 2232898853 251 d0 /
      data wgk (  6) / 0.0143697295 0704580481 2451432443 580 d0 /
      data wgk (  7) / 0.0169208891 8905327262 7572289420 322 d0 /
      data wgk (  8) / 0.0194141411 9394238117 3408951050 128 d0 /
      data wgk (  9) / 0.0218280358 2160919229 7167485738 339 d0 /
      data wgk ( 10) / 0.0241911620 7808060136 5686370725 232 d0 /
      data wgk ( 11) / 0.0265099548 8233310161 0601709335 075 d0 /
      data wgk ( 12) / 0.0287540487 6504129284 3978785354 334 d0 /
      data wgk ( 13) / 0.0309072575 6238776247 2884252943 092 d0 /
      data wgk ( 14) / 0.0329814470 5748372603 1814191016 854 d0 /
      data wgk ( 15) / 0.0349793380 2806002413 7499670731 468 d0 /
      data wgk ( 16) / 0.0368823646 5182122922 3911065617 136 d0 /
      data wgk ( 17) / 0.0386789456 2472759295 0348651532 281 d0 /
      data wgk ( 18) / 0.0403745389 5153595911 1995279752 468 d0 /
      data wgk ( 19) / 0.0419698102 1516424614 7147541285 970 d0 /
      data wgk ( 20) / 0.0434525397 0135606931 6831728117 073 d0 /
      data wgk ( 21) / 0.0448148001 3316266319 2355551616 723 d0 /
      data wgk ( 22) / 0.0460592382 7100698811 6271735559 374 d0 /
      data wgk ( 23) / 0.0471855465 6929915394 5261478181 099 d0 /
      data wgk ( 24) / 0.0481858617 5708712914 0779492298 305 d0 /
      data wgk ( 25) / 0.0490554345 5502977888 7528165367 238 d0 /
      data wgk ( 26) / 0.0497956834 2707420635 7811569379 942 d0 /
      data wgk ( 27) / 0.0504059214 0278234684 0893085653 585 d0 /
      data wgk ( 28) / 0.0508817958 9874960649 2297473049 805 d0 /
      data wgk ( 29) / 0.0512215478 4925877217 0656282604 944 d0 /
      data wgk ( 30) / 0.0514261285 3745902593 3862879215 781 d0 /
      data wgk ( 31) / 0.0514947294 2945156755 8340433647 099 d0 /
c
c           list of major variables
c           -----------------------
c
c           centr  - mid point of the interval
c           hlgth  - half-length of the interval
c           dabsc  - abscissa
c           fval*  - function value
c           resg   - result of the 30-point gauss rule
c           resk   - result of the 61-point kronrod rule
c           reskh  - approximation to the mean value of f
c                    over (a,b), i.e. to i/(b-a)
c
c           machine dependent constants
c           ---------------------------
c
c           epmach is the largest relative spacing.
c           uflow is the smallest positive magnitude.
c
      epmach = d1mach(4)
      uflow = d1mach(1)
c
      centr = 0.5d+00*(b+a)
      hlgth = 0.5d+00*(b-a)
      dhlgth = abs(hlgth)
c
c           compute the 61-point kronrod approximation to the
c           integral, and estimate the absolute error.
c
c***first executable statement  dqk61
      resg = 0.0d+00
      fc = f(centr)
      resk = wgk(31)*fc
      resabs = abs(resk)
      do 10 j=1,15
        jtw = j*2
        dabsc = hlgth*xgk(jtw)
        fval1 = f(centr-dabsc)
        fval2 = f(centr+dabsc)
        fv1(jtw) = fval1
        fv2(jtw) = fval2
        fsum = fval1+fval2
        resg = resg+wg(j)*fsum
        resk = resk+wgk(jtw)*fsum
        resabs = resabs+wgk(jtw)*(abs(fval1)+abs(fval2))
   10 continue
      do 15 j=1,15
        jtwm1 = j*2-1
        dabsc = hlgth*xgk(jtwm1)
        fval1 = f(centr-dabsc)
        fval2 = f(centr+dabsc)
        fv1(jtwm1) = fval1
        fv2(jtwm1) = fval2
        fsum = fval1+fval2
        resk = resk+wgk(jtwm1)*fsum
        resabs = resabs+wgk(jtwm1)*(abs(fval1)+abs(fval2))
  15    continue
      reskh = resk*0.5d+00
      resasc = wgk(31)*abs(fc-reskh)
      do 20 j=1,30
        resasc = resasc+wgk(j)*(abs(fv1(j)-reskh)+abs(fv2(j)-reskh))
   20 continue
      result = resk*hlgth
      resabs = resabs*dhlgth
      resasc = resasc*dhlgth
      abserr = abs((resk-resg)*hlgth)
      if(resasc.ne.0.0d+00.and.abserr.ne.0.0d+00)
     *  abserr = resasc*min(0.1d+01,(0.2d+03*abserr/resasc)**1.5d+00)
      if(resabs.gt.uflow/(0.5d+02*epmach)) abserr = max
     *  ((epmach*0.5d+02)*resabs,abserr)
      return
      end
      subroutine dqpsrt(limit,last,maxerr,ermax,elist,iord,nrmax)
c***begin prologue  dqpsrt
c***refer to  dqage,dqagie,dqagpe,dqawse
c***routines called  (none)
c***revision date  810101   (yymmdd)
c***keywords  sequential sorting
c***author  piessens,robert,appl. math. & progr. div. - k.u.leuven
c           de doncker,elise,appl. math. & progr. div. - k.u.leuven
c***purpose  this routine maintains the descending ordering in the
c            list of the local error estimated resulting from the
c            interval subdivision process. at each call two error
c            estimates are inserted using the sequential search
c            method, top-down for the largest error estimate and
c            bottom-up for the smallest error estimate.
c***description
c
c           ordering routine
c           standard fortran subroutine
c           real*8 version
c
c           parameters (meaning at output)
c              limit  - integer
c                       maximum number of error estimates the list
c                       can contain
c
c              last   - integer
c                       number of error estimates currently in the list
c
c              maxerr - integer
c                       maxerr points to the nrmax-th largest error
c                       estimate currently in the list
c
c              ermax  - real*8
c                       nrmax-th largest error estimate
c                       ermax = elist(maxerr)
c
c              elist  - real*8
c                       vector of dimension last containing
c                       the error estimates
c
c              iord   - integer
c                       vector of dimension last, the first k elements
c                       of which contain pointers to the error
c                       estimates, such that
c                       elist(iord(1)),...,  elist(iord(k))
c                       form a decreasing sequence, with
c                       k = last if last.le.(limit/2+2), and
c                       k = limit+1-last otherwise
c
c              nrmax  - integer
c                       maxerr = iord(nrmax)
c
c***end prologue  dqpsrt
c
      real*8 elist,ermax,errmax,errmin
      integer i,ibeg,ido,iord,isucc,j,jbnd,jupbn,k,last,limit,maxerr,
     *  nrmax
      dimension elist(last),iord(last)
c
c           check whether the list contains more than
c           two error estimates.
c
c***first executable statement  dqpsrt
      if(last.gt.2) go to 10
      iord(1) = 1
      iord(2) = 2
      go to 90
c
c           this part of the routine is only executed if, due to a
c           difficult integrand, subdivision increased the error
c           estimate. in the normal case the insert procedure should
c           start after the nrmax-th largest error estimate.
c
   10 errmax = elist(maxerr)
      if(nrmax.eq.1) go to 30
      ido = nrmax-1
      do 20 i = 1,ido
        isucc = iord(nrmax-1)
c ***jump out of do-loop
        if(errmax.le.elist(isucc)) go to 30
        iord(nrmax) = isucc
        nrmax = nrmax-1
   20    continue
c
c           compute the number of elements in the list to be maintained
c           in descending order. this number depends on the number of
c           subdivisions still allowed.
c
   30 jupbn = last
      if(last.gt.(limit/2+2)) jupbn = limit+3-last
      errmin = elist(last)
c
c           insert errmax by traversing the list top-down,
c           starting comparison from the element elist(iord(nrmax+1)).
c
      jbnd = jupbn-1
      ibeg = nrmax+1
      if(ibeg.gt.jbnd) go to 50
      do 40 i=ibeg,jbnd
        isucc = iord(i)
c ***jump out of do-loop
        if(errmax.ge.elist(isucc)) go to 60
        iord(i-1) = isucc
   40 continue
   50 iord(jbnd) = maxerr
      iord(jupbn) = last
      go to 90
c
c           insert errmin by traversing the list bottom-up.
c
   60 iord(i-1) = maxerr
      k = jbnd
      do 70 j=i,jbnd
        isucc = iord(k)
c ***jump out of do-loop
        if(errmin.lt.elist(isucc)) go to 80
        iord(k+1) = isucc
        k = k-1
   70 continue
      iord(i) = last
      go to 90
   80 iord(k+1) = last
c
c           set maxerr and ermax.
c
   90 maxerr = iord(nrmax)
      ermax = elist(maxerr)
      return
      end
