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

	static struct point e_zerodich2(struct point A, struct point B, double dl0s, double dos, double zs);

	/****************************************************************/
	/* nom: e_zeroamp */
	/* auteur: Jean-Paul Kneib */
	/* date: 10/02/92 */
	/* place: Toulouse */
	/****************************************************************/
	/* Return the critical line position between A and B
	* Global variables used :
	* in e_amp() : G, lens, lens_table
	* in e_zerodich2() : G, lens, lens_table
	*/
	struct point e_zeroamp(struct point A, struct point B, double dl0s, double dos, double zs)
	{
	struct point C;

	/order A and B so that amp(A)>amp(B)/
	if ( e_amp(&A, dl0s, dos, zs) > e_amp(&B, dl0s, dos, zs))
	{
	C = A;
	A = B;
	B = C;
	};

	return( e_zerodich2(&A, &B, dl0s, dos, zs) );
	}

	/****************************************************************/
	/* Return the critical line position between A and B
	* Global variables used :
	* - in e_amp() : G, lens, lens_table
	*/
	static struct point e_zerodich2(struct point A, struct point B, double dl0s, double dos, double zs)
	{
	double am;
	struct point M;

	M = milieu(A, B);
	am = e_amp(&M, dl0s, dos, zs);
	if ( dist(A, B) < PREC_ZERO \|\| fabs(am) < PREC_ZERO )
	return(M);
	else if ( am * e_amp(A, dl0s, dos, zs) > 0 )
	/M and A are on the same side of the critical line (same parity)/
	return(e_zerodich2(&M, B, dl0s, dos, zs));
	else
	return(e_zerodich2(A, &M, dl0s, dos, zs));
	}