#!/bin/csh -f
#+
# grand -- generate a normal (Gaussian) random value
#
# Purpose:
#	Returns a normally-distributed (i.e., drawn from a Gaussian
#	normal distribution with mean of 0 and stddev of 1), using as
#	a seed either the argument provided or, if none, the time of day.
#
# Usage:
#	grand [seed]
# 
# Arguments:
#	seed = INTEGER seed value for random number generator
# 
# Exit values:
#	 0 = normal completion
#	 1 = wrong number of arguments
#
# Example:
#	1) Return random normal values:
#		punaluu{lris}180: ./grand
#		0.564412
#		punaluu{lris}181: ./grand
#		-0.802072
#	   Note that the values differ because the process number (used
#	   by default as the random generator's seed) changed.
#
# 	2) Return a random value for a given seed:
#		punaluu{lris}183: ./grand 12345
#		1.08078
#		punaluu{lris}184: ./grand 12345
#		1.08078
#	   Note that the values are the same when the same seed is used.
#-
# Modification history:
#	2000-Jul-03	GDW	Original version
#-----------------------------------------------------------------------

# parse command line args...
if ( $#argv == 0 ) then
  @ seed = $$			# use Unix process number
else if ( $#argv == 1 ) then
  @ seed = $1			# use argument
else
  echo "Usage: grand [seed]"
  exit 1
endif

gawk "BEGIN{dum = srand(${seed}) ; \
	pi = atan2(0,-1) ; \
	print sqrt(-2.*log(rand()))*cos(2.*pi*rand())}"