help with contour plot

Trying to plot.

The equation is:

A tip in polar coordinates:

And my code:

(The picture above is how it is supposed to look9

[Walter Roberson]

Note that volunteers are seldom interested in typing in code from pictures of code. Make it easier for the volunteers by providing actual code.

Answer 1

[Walter Roberson]

Your line with == computes whether each element of Z happens to have a particular and exact relationship to X and Y. Once it has done that computation of whether there is a match or not, your code then throws away that computation, having wasted time but otherwise not having done anything useful.

I would suggest to you,

Z2 = X.^2 + Y.^2 + 1;
surf(X, Y, Z2)

[Hanna Sundling]

I changed as you suggested but the biggest problem is that when I plot is that I only get this:

And not the full object, and I do not know why.

[Walter Roberson]

Your sample diagram has negative Z values. Your suggested code of surf(X, Y, Z.^2) has only positive Z (unless Z includes values with purely imaginary components. You need to go back and decide whether using X, Y, Z^2 is correct surfing.

Hint: if P^2 = something, then it implies that P of both +sqrt(something) and -sqrt(something) are valid.

[Hanna Sundling]

I do not understand how I sholud change.

I tried writing Z1 = Z2.^2 an then surf(X,Y,Z1)

[Walter Roberson]

surf() one thing. "hold on". surf() another thing that is mirror in Z.