o_chi_flux.c
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	#include<stdio.h>
	#include<math.h>
	#include<fonction.h>
	#include<constant.h>
	#include<dimension.h>
	#include<structure.h>

	/****************************************************************/
	/* nom: o_chi_flux */
	/* auteur: Ghislain Golse */
	/* date: 10/99 */
	/* place: Toulouse */
	/****************************************************************
	* Calcul de chi2 deduit de la difference de flux entre celui
	* donne par la source "moyenne" et celui de l'image
	*
	* mag = -2.5 log f
	* dmag = -2.5 df / f --> df = abs( dmag * f / 2.5 )
	*
	* Global variables used :
	* - I
	*/
	void o_chi_flux(struct galaxie arclet, double fluxS, double da, double *sig2flux)
	{
	double Dflux;
	const extern struct g_image I;

	// If Dmag is very small compared to flux then
	// the approximation is dfv = ln10/2.5dMfv
	Dflux = I.Dmag * arclet->flux / 2.5;

	sig2flux = Dflux Dflux;
	*da = arclet->flux - fluxS / arclet->A;

	}