c **********************************************************
      program interpolate
c **********************************************************

c  Read a 360x180 file and interpolate the values to a
c  180x90 grid.  

      dimension nb(360,180),ns(180,90)
      character*50 infile,outfile
      character*30 infrmt,outfrmt
      character*80 header

      write (*,*) ' '
      write (*,*) ' Enter name of 360x180 input file: '
      write (*,*) ' '
      read (*,17) infile
   17 format (a)

      write (*,*) ' '
      write (*,*) ' Enter input format of 360x180 file, '
      write (*,*) ' e.g. (f8.2) or (180i1): '
      write (*,*) ' '
      read (*,17) infrmt

      write (*,*) ' '
      write (*,*) ' Enter name of 180x90 output file: '
      write (*,*) ' '
      read (*,17) outfile

      write (*,*) ' '
      write (*,*) ' Enter output format of 180x90 file, '
      write (*,*) ' e.g. (f8.2) or (180i1): '
      write (*,*) ' '
      read (*,17) outfrmt

      open (7,file=infile,status='old')

      read (7,18) header
   18 format (a80)
      do 40 j=1,180,1
        read (7,infrmt) (nb(i,j),i=1,360,1)
   40 continue

      open (8,file=outfile,status='new',recl=4000)

c  Interpolate 360x180 field to 180x90 with values ranging from
c  89, 87, ... , -89 deg. lat. and -179, -177, ..., 179 deg. lon.

      do 970 j=1,90,1
        do 970 i=1,180,1
          ns(i,j) = 0.25*( float(nb(2*i-1,2*j-1)) +
     &                        float(nb(2*i,2*j-1)) +
     &                        float(nb(2*i-1,2*j)) +
     &                        float(nb(2*i,2*j)) )
  970 continue

      write (8,18) header
      do 980 j=1,90,1
        write (8,outfrmt) (ns(i,j),i=1,180,1)
  980 continue

      stop
      end