program subtrc

*** subtract one grid from another

      implicit double precision(a-h,o-z)
      character*188 fname
      integer hrec1(9999),hrec2(9999)
      real*4  zrec1(9999),zrec2(9999)
      equivalence(hrec1(1),zrec1(1))
      equivalence(hrec2(1),zrec2(1))

      lin1=1
      lin2=2
      lout=3

      write(6,*) 'program subtrc'

      write(6,3)
    3 format('Enter "plus" input file:  ',$)
      read(5,1) fname
    1 format(a)
      open(lin1,file=fname,status='old',form='unformatted')

      write(6,4)
    4 format('Enter "minus" input file: ',$)
      read(5,1) fname
      open(lin2,file=fname,status='old',form='unformatted')

      write(6,2)
    2 format('Enter "a-b" output file:   ',$)
      read(5,1) fname
      open(lout,file=fname,status='new',form='unformatted')

      read(lin1) glamn1,glomn1,dgla1,dglo1,nla1,nlo1,ikind1
      read(lin2) glamn2,glomn2,dgla2,dglo2,nla2,nlo2,ikind2

*** check compatability

      if(dabs(glomn1-glomn2).gt.1.d-7) stop 1
      if(dabs(glamn1-glamn2).gt.1.d-7) stop 6
      if(dabs(dgla1 -dgla2 ).gt.1.d-7) stop 2
      if(dabs(dglo1 -dglo2 ).gt.1.d-7) stop 3
      if(nlo1  .ne.nlo2  ) stop 4
      if(nla1  .ne.nla2  ) stop 7
      if(ikind1.eq.0.and.ikind2.ne.0.or.
     *   ikind2.eq.0.and.ikind1.ne.0) stop 5

      write(lout) glamn1,glomn1,dgla1,dglo1,nla1,nlo1,ikind1
      if(ikind1.eq.0) then
        do 10 irow=1,nla1
        read (lin1) (hrec1(i),i=1,nlo1)
        read (lin2) (hrec2(i),i=1,nlo1)
        do 11 i=1,nlo1
   11   hrec1(i)=hrec1(i)-hrec2(i)
   10   write(lout) (hrec1(i),i=1,nlo1)
      else
        do 20 irow=1,nla1
        read (lin1) (zrec1(i),i=1,nlo1)
        read (lin2) (zrec2(i),i=1,nlo1)
        do 21 i=1,nlo1
   21   zrec1(i)=zrec1(i)-zrec2(i)
   20   write(lout) (zrec1(i),i=1,nlo1)
      endif

      stop
      end