clc
close all
clear all
f = @(x, y) x.*sqrt(y);
figure
hold on
xlabel('x')
ylabel('y')
zlabel('z')
I = [0 6 0 6];
fsurf(f, I)
T0 = @(x, y) 2 + 0*x + 0*y;
fsurf(T0, I)
T1 = @(x, y) -1 + 2*x + 1/4*y;
fsurf(T1, I)
T2 = @(x, y) -1 + 2*x + 1/4*y + ...
    1/4*(x - 1).*(y - 4) - ...
    1/64*(y - 4).^2;
fsurf(T2, I)