linspace error while trying to plot

Question

fartash2020 2017-11-30

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/370311-linspace-error-while-trying-to-plot

评论： Walter Roberson 2017-11-30

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

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,

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Answer 1

Walter Roberson 2017-11-30

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/370311-linspace-error-while-trying-to-plot#answer_294034

在 MATLAB Online 中打开

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.

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fartash2020 2017-11-30

编辑：Walter Roberson 2017-11-30

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 2017-11-30

在 MATLAB Online 中打开

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.

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