forward(YREAL xd, YREAL yd, YREAL ud, YREAL vd)
{
	
	//what we had up to 01/04
	/*YS1=xd+rdtflo*ud+xd*rdtflo*(ur_dx+ur_dy);//mot cle YS1: yao sortie 1
	printf("xd=%f 2term=%f 3term=%f\n",xd,rdtflo*ud,xd*rdtflo*(ur_dx+ur_dy));
	YS2=yd+rdtflo*vd+yd*rdtflo*(vr_dx+vr_dy);*/
	
	//what we should have corrected on 04/04
	YS1=xd+rdtflo*ud+rdtflo*(xd*ur_dx+yd*ur_dy);
	YS2=yd+rdtflo*vd+rdtflo*(xd*vr_dx+yd*vr_dy);
	//printf("ud=%f\n",ud);
}

backward(YREAL xd, YREAL yd, YREAL ud, YREAL vd)
{
	/*YJ1I1=1+rdtflo*(ur_dx+ur_dy);   //mot cle, les entrees du gradient du out par rapport au in, dYs1/dx,y,u,v
	YJ1I2=0;
	YJ1I3=rdtflo;
	YJ1I4=0;
	
	YJ2I1=0; //dYs2/dx,y,u,v
	YJ2I2=1+rdtflo*(vr_dx+vr_dy);
	YJ2I3=0;
	YJ2I4=rdtflo;*/
	
	
	//what we sould have corrected on 04/04
	YJ1I1=1+rdtflo*ur_dx;   
    YJ1I2=rdtflo*ur_dy;
	YJ1I3=rdtflo;
	YJ1I4=0;
	
	YJ2I1=rdtflo*vr_dx; 
	YJ2I2=1+rdtflo*vr_dy;
	YJ2I3=0;
	YJ2I4=rdtflo;
	
}