function gauss_distr,n,sig
; produces gaussian distribution of random numbers
;   mean=0, var=total(gd^2)/n)=1.
; from num recipes, pg 203 (GASDEV routine)

u=randomu(seed,n*6)

gd=fltarr(n)

k=0L
j=0L
while k lt n do begin
  v1=2.*u(j)-1.
  v2=2.*u(j+1)-1.
  r=v1^2+v2^2
  if r ge 1. then goto,skip
  fac=sqrt(-2.*alog(r)/r)
  gd(k)=v1*fac
  gd((k+1) < (n-1))=v2*fac
  k=k+2
skip:
  j=j+2
endwhile

return,gd
end