linspace error while trying to plot

Dear all,

I have written a code for linspace I want a 3D plot of it:

% First we set the constants:

kd=6;

lambda= 0.01;

Delta_E=0.02;

% Then we write down the Formulas:

z=linspace(-1,1,200);

kappa=linspace(0,1,200);

q=((Delta_E)+(lambda.*z)+(((sqrt((1+z)./2)).*exp(-(kd.*(sqrt(2.*lambda'.*(1+z))))))).*(kappa.*(sqrt((1-z)./(1+z)))-(sqrt((1+z)./(1-z )))));

% Now we plot q(Z,kappa) vs Z and kappa :

figure(1)

mesh(z,kappa,q)

% title('kd=6');

   xlabel('Z');

   ylabel('lambda');

   zlabel('q)');

I think that my "q" must have 200*200 matrix, but it is not. Its gives just 1*200.

I would highly appreciate if you help me.

Thanks,

Answer 1

[Walter Roberson]

Change

z=linspace(-1,1,200);
kappa=linspace(0,1,200);

to

Z = linspace(-1,1,200);
KAPPA = linspace(0,1,200);
[z, kappa] = meshgrid(Z, KAPPA);

Note: you have

     ylabel('lambda');

which is not correct. Your lambda is a constant. Your y axes is kappa, not lambda.

[fartash2020]

Dear Walter,

Thank you very much for your answer. Also, I want to plot Z vs kappa for the time that q=0. in 2D of course.

Best Regards,

[Walter Roberson]

contour(z, kappa, q, [0 0])

the [0 0] is a trick that has to be used when you are only asking for one contour value; if you were to try to pass in the scalar 0 at that point, it would try to interpret the scalar 0 as the number of contour levels to draw.