c
c     this is an example program to compute the Boltzman ratio for
c     neutral hydrogen from the n=2 to the n=1 excitation level and the
c     n=3 to n=1 level
c

      PROGRAM example

      implicit none
      integer           i
      double precision  m,ratio

      include           'example.com'


      temp   = 1.e4

      DO 11 i=1,3
        m      =  float(i)    
        g(i)   = 2.0*m**2
        chi(i) = 13.6*(1.0-1.0/m**2)
        WRITE(6,600) i,g(i),chi(i)
 11   CONTINUE


      OPEN(unit=1,file='example.dat')
      WRITE(1,601)

      DO 15 i=2,3
        CALL boltzman(i,ratio)
        WRITE(1,602) temp,i,ratio
 15   CONTINUE

      CLOSE(unit=1)
  

 600  FORMAT(1x,i3,1x,f8.2,1x,f7.3)
 601  FORMAT(4x,'Temp, K',3x,'i',3x,'n(i)/n(1)')
 602  FORMAT(1x,f10.1,1x,i3,1x,1pe11.3)

      STOP
      END

c     ...........................................................

c     this is the subroutine that computes the boltzman equation
c     on return, R has the desired value

      SUBROUTINE boltzman(i,r)

      implicit none
      integer            i
      double precision   r,theta

      include         'example.com'

      theta =  5040./temp 
      r     = (g(i)/g(1)) * 10**(-theta*chi(i))
      
      RETURN
      END

c     ...........................................................