function gaussdev(idum)
	integer idum
	real gaussdev
c  uses RAN1 
c  to make a normally distributed deviate with zero mean and unit variance
c
	integer iset
	real fac,gset,rsq,v1,v2,ran1
	save iset,gset
	data iset/0/
	if(iset.eq.0) then
1		v1=2.*ran1(idum)-1
		v2=2.*ran1(idum)-1
		rsq=v1**2+v2**2
		if(rsq.ge.1..or.rsq.eq.0.) goto 1
		fac=sqrt(-2.*log(rsq)/rsq)
		gset=v1*fac
		gaussdev=v2*fac
		iset=1
	else
		gaussdev=gset
		iset=0
	endif
	return
	end