function randgs (xmean, sd)
c
c generate a normally distributed random number, i.e., generate random
c numbers with a gaussian distribution.  these random numbers are not
c exceptionally good -- especially in the tails of the distribution,
c but this implementation is simple and suitable for most applications.
c see r. w. hamming, numerical methods for scientists and engineers,
c mcgraw-hill, 1962, pages 34 and 389.
c
c             input arguments --
c xmean  the mean of the gaussian distribution.
c sd     the standard deviation of the gaussian function
c          exp (-1/2 * (x-xmean)**2 / sd**2)
c
      external rand
c
      randgs = -6.
      do 10 i=1,12
        randgs = randgs + rand(0.)
 10   continue
c
      randgs = xmean + sd*randgs
c
      return
      end