c-------------------------------------------------
c     Author:  Brian Martin
c     modified last:  Nov.5, 2004.
c-------------------------------------------------

c-------------------------------------------------
c     a program to calculate the sum of 
c     Bessel Functions.
c     The equation is:
c     V(x) = 2 *sum(n=-inf..inf)U(sqrt(x^2+(nw)^2))
c     Where U(r) is defined by:
c     U(r) = const. * Ko(r)
c     Ko is the 0th order bessel function
c-------------------------------------------------

      program test
      implicit none
c-------------------------------------------------
c     Variable declarations
c-------------------------------------------------
c     used for command line argument parsing
      integer iargc, i4arg
      real*8  r8arg

      real*8   calcv
      external calcv
c     this is the x in the equation
      real*8 x
      real*8 v

c     index variables
      integer n, range
      real*8  e, w
c-------------------------------------------------

c-------------------------------------------------
c     make sure there is at least one argument
      if (iargc() .lt. 1) go to 1000
c-------------------------------------------------

c-------------------------------------------------
c     Argument Parsing
c-------------------------------------------------
      range = i4arg(1,-1) * 10000
      e     = r8arg(2, 1.0d-6)
      w     = r8arg(3, 1.0d0)

      do n = -1*range, range
         x = n / 1.0d4
         call calcv(v,x,w,e)
c     output the sum
         write(*,*) x, v
      end do

      stop

 1000 continue
      write(0,*) 'usage: test <n> [<e>]'
      write(0,*) '       nmax is the max of n'
      write(0,*) '       e is tolerance parameter'
      write(0,*) '           default is 1.0d-6'
      stop

      end