void bcuint(y,y1,y2,y12,x1l,x1u,x2l,x2u,x1,x2,ansy,ansy1,ansy2)
float y[],y1[],y2[],y12[],x1l,x1u,x2l,x2u,x1,x2,*ansy,*ansy1,*ansy2;
{
	int i;
	float t,u,d1,d2,**c,**matrix();
	void bcucof(),nrerror(),free_matrix();

	c=matrix(1,4,1,4);
	d1=x1u-x1l;
	d2=x2u-x2l;
	bcucof(y,y1,y2,y12,d1,d2,c);
	if (x1u == x1l || x2u == x2l) nrerror("Bad input in routine BCUINT");
	t=(x1-x1l)/d1;
	u=(x2-x2l)/d2;
	*ansy=(*ansy2)=(*ansy1)=0.0;
	for (i=4;i>=1;i--) {
		*ansy=t*(*ansy)+((c[i][4]*u+c[i][3])*u+c[i][2])*u+c[i][1];
		*ansy2=t*(*ansy2)+(3.0*c[i][4]*u+2.0*c[i][3])*u+c[i][2];
		*ansy1=u*(*ansy1)+(3.0*c[4][i]*t+2.0*c[3][i])*t+c[2][i];
	}
	*ansy1 /= d1;
	*ansy2 /= d2;
	free_matrix(c,1,4,1,4);
}