What's wrong with my distribution function?

I'm trying to draw a chi-square distribution in XYZ space. Chi-square distribution in Geogebra is supposed to be (with different index k):

That means, it is supposed to be a central-symmetric, volcano-shaped figure.

Here comes the code:

X = -100 : 1 : 100;
Y = -100 : 1 : 100;

k = 4;

G = gamma(k/2);

[ XX, YY ] = meshgrid( X, Y );

A = ( XX ).^2 + ( YY ).^2;

A = sqrt (A);

Z = (A^(k/2 - 1) * exp(-A / 2)) / ( 2^(k/2) * G );

figure, mesh(X, Y, Z);

Very unfortunately, the figure I generated is:

What exactly is wrong with my code?

[Shing Ho Lin]

It is most probably a silly question, but I just get stuck into this. Very much appreciated for any possible answer:)

Answer 1

[VBBV]

X = -100 : 1 : 100;
Y = -100 : 1 : 100;
k = 4;
G = gamma(k/2)

G = 1

[ XX, YY ] = meshgrid( X, Y );
A = ( XX ).^2 + ( YY ).^2;
A = sqrt (A);
Z = (A.^(k/2-1).*exp(-A / 2))./(2^(k/2)* G); % use element wise operator 
mesh(X, Y, Z);
axis([-20 20 -100 100 0 0.2])

[VBBV]

use element wise operator .* in the expression

[Shing Ho Lin]

Thank you so much. Apparently I was way to idiot :(

[VBBV]

Thanks is accpeting answer, :) ,