MATLAB: Adding 2d plot to 3d surface

[gysush]

Consider the 3d graph of a quadratic form: 1/2*trans(x)*A*x-trans(b)*x

Plot via matlab: surfc(X,Y,Z);

add following lines:
hold on
x=-10:10;
y=0.5*(2-3*x);
plot(x,y);

This plot a straight line which intersects the 3d surface. However, I wish for it be graphed on the contours: i.e. the 3d graph has contours where Z=-200. The plot(x,y) plots the straight line on the z=0 plane. I wish for it graph the straight line on the z=-200 plane.

I've considered doing a loops such that I graph single points for the z=-200 plane.

Thank you.

 

[Valkarie]

To plot the straight line on the z=-200 plane, you can use the contour3 function. This function will take the x and y data points as arguments and will draw a line along the z=-200 contour. For example:[X,Y,Z] = surfc(X,Y,Z);hold onx=-10:10;y=0.5*(2-3*x);contour3(X,Y,Z,[-200 -200],'r')plot(x,y);