c 
c  The rest of the 2-d program 
c 
      double precision function diff2d( a, b, nx, sx, ex, sy, ey ) 
      integer nx, sx, ex, sy, ey 
      double precision a(sx-1:ex+1, sy-1:ey+1), b(sx-1:ex+1, sy-1:ey+1) 
c 
      double precision sum 
      integer i, j 
c 
      sum = 0.0d0 
      do 10 j=sy,ey 
         do 10 i=sx,ex 
            sum = sum + (a(i,j) - b(i,j)) ** 2 
 10      continue 
c       
      diff2d = sum 
      return 
      end