c===========================================================
c     Demonstrates sample use of SLATEC routine dgaus8
c     to integrate a real function of one variable
c     over a finite interval.
c
c     % maple
c     > Digits := 16:
c     > evalf();
c
c     SUBROUTINE DGAUS8 (FUN, A, B, ERR, ANS, IERR)
c===========================================================
      program     tdgaus8

      implicit    none

      integer     iargc
      real*8      r8arg
      logical     ltrace

      external    fun
      real*8      fun

      real*8      default_err
      parameter ( default_err = 1.0d-8 )

      real*8      a,  b,  err,  ans
      integer     ierr
   
c-----------------------------------------------------------
c     Argument parsing.
c-----------------------------------------------------------
      if( iargc() .lt. 2 ) go to 900
      a = r8arg(1,-99.0d0)
      b = r8arg(2,-99.0d0)
      err = r8arg(3,default_err)
      ltrace = iargc() .gt. 3

      if( ltrace ) then
         write(0,*) 'tdgaus8: a = ', a
         write(0,*) 'tdgaus8: b = ', b
         write(0,*) 'tdgaus8: err = ', err
      end if
      call dgaus8 (fun, a, b, err, ans, ierr)
      if( ierr .ne. 1 ) then
         write(0,*) 'tdgaus8: Requested error criterion '//
     &              'could not be achieved'
      end if
      write(*,*) ans

      stop

 900  continue
         write(0,*) 'usage: tdgaus8 <a> <b> [<err> <trace>]'
         write(0,*) ' '
         write(0,*) 
     &      '       Computes aproximate value of Int(exp(-x^2),x=a..b)'
         write(0,*) 
     &      '       with an approximate error <err>'                    
      stop

      end

      real*8 function fun(x)
         implicit  none
         real*8    x

         fun = exp(-x**2)

         return

      end