struct Linear_interp : Base_interp
{
	Linear_interp(VecDoub_I &xv, VecDoub_I &yv)
		: Base_interp(xv,&yv[0],2)  {}
	Doub rawinterp(Int j, Doub x) {
		if (xx[j]==xx[j+1]) return yy[j];
		else return yy[j] + ((x-xx[j])/(xx[j+1]-xx[j]))*(yy[j+1]-yy[j]);
	}
};