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      implicit none
 
      integer ni,nj 
      parameter(ni=361,nj=181)

      character*20 myLonStr, myLatStr
      integer iargc, i, j
      real lat(nj),lon(ni),val(ni,nj)
      real interp_lat, interp_lon, interp_val
      real dlat,dlon

c
c check the 2 input arugments for longitude and latitude
c
      if (iargc() .ne. 2) then
         print *, 'Usage: nameOfExecutable interp_lon interp_lat'
         stop
      endif

c
c read the input arguments as strings
c
      call getarg(1,myLonStr)
      call getarg(2,myLatStr)

c
c convert the strings to real numbers
c
      read(myLonStr, *) interp_lon
      read(myLatStr, *) interp_lat

c
c define latitude and longitude grid in 0.5-deg spacing
c
      dlat=0.5
      dlon=0.5

      do j=1,nj
         lat(j)=(j-1)*dlat
      enddo

      do i=1,ni
         lon(i)=(i-1)*dlon
      enddo

c
c define 2d value being interpolated
c
      do j=1,nj
         do i=1,ni
            val(i,j)=(i-1)*(j-1)
         enddo
      enddo

c
c call the bilinear subroutine
c
      call bilinear_sub(ni, nj, dlon, dlat, lon, lat, val,
     &                  interp_lon, interp_lat, interp_val)

      print*,'interpolated value from bilinear_sub = ', interp_val

      end