function sigma_x,bins,conc
;Title:		sigma_x.pro
;Purpose:	Function to calculate the logarithmic spread of the
;			liquid particle size distribution.
;
;Inputs:	bins:	bin sizes in microns.
;			conc:	concentration per bin (1/cm3)
;
;Outputs:	sigma:	logarithmic spread of the particle size dist'n.
;
;Author:	Matthew Shupe
;Date:		4/20/00
;---------------------------------------------------------------

N=total(conc)   ;Total concentration
if N ge 10 and N lt 10000 then begin
	lgN=total(conc*alog(bins))/N
	s0=total(conc*((alog(bins))^2))
	sigsq= s0/N - lgN^2
	if sigsq gt 0 then sigma=sqrt(sigsq) else sigma=0
endif else sigma=0
return,sigma
end