program make_user_spectral_grid
      implicit none
      include 'max.inc'
c
c     Purpose: to generate a user-defined spectral grid, recorded
c     into "user_spectral_grid.in"
c     Remember that this grid should contain values in every narrowband
c     defined by the "narrowbands.in" input data file.
c
c     Variables
      double precision nu_min,nu_max,dnu
c     temp
      integer i
      double precision nu
      character*(Nchar_mx) sgrid_file
c     label
      integer strlen
      character*(Nchar_mx) label
      label='program make_user_spectral_grid'

c     ---------------------------------------------------------------------------------
c     Simple scheme: use a constant spectral step in the [nu_min,nu_max] interval
c     
c     Lower limit
      nu_min=0.0D+0 ! inv. cm
c     Higher limit
      nu_max=12.0D+3 ! inv. cm
c     Spectral step
      dnu=1.0D-2 ! inv. cm
c     ---------------------------------------------------------------------------------

c     spectral grid filename
      sgrid_file='./user_spectral_grid.in'

c     coherence check
      if (nu_max.le.nu_min) then
         call error(label)
         write(*,*) 'nu_max=',nu_max
         write(*,*) 'should be higher than nu_min=',nu_min
         stop
      endif
      if (dnu.gt.nu_max-nu_min) then
         call error(label)
         write(*,*) 'dnu=',dnu
         write(*,*) '< mu_max-mu_min=',nu_max-nu_min
         stop
      endif
      
c     generate file
      write(*,*) 'Now recording spectral grid...'
      nu=nu_min
      open(10,file=sgrid_file(1:strlen(sgrid_file)))
      i=0
      do while (nu.lt.nu_max)
         nu=nu_min+i*dnu
         write(10,*) nu
         i=i+1
      enddo ! while (nu<=nu_max)
      close(10)
      write(*,*) 'Output file was succesfuly generated:'
      write(*,*) sgrid_file(1:strlen(sgrid_file))

      end