Surf from a numerical array

Suppose I solve a PDE and obtain a solution in 2D say . If I do surf(u) I get a picture of the whole thing. Can I change the values of the axis to correspond to the actual values of interest? Currently the axis values just represent the number of data points, so I want to change that to actual values of interest.

Answer 1

[Voss]

Yes. You can use the xlim and ylim functions to set the axes limits to the actual region of interest.

Example:

% some matrix
z = peaks(100);

% the whole thing
figure();
surf(z) 
xlabel('x')
ylabel('y')
zlabel('z')

% the actual region of interest
figure();
surf(z)
xlabel('x')
ylabel('y')
zlabel('z')
xlim([30 75])
ylim([50 90])

[Mat Hunt]

This makes the actual surface dissipear.

[Voss]

Hmm. It appears not to disappear in the code I ran above. Maybe you've chosen some xlim and/or ylim that are outside the limits of the surface.

[Mat Hunt]

It appears that you gave misunderstood my question. The labels that you get when you just do surf(array) is the number of entries. I want to relabel these to actual physical values.

[Voss]

"It appears that you [h]ave misunderstood my question."

Entirely likely.

"The labels that you get when you just do surf(array) is the number of entries. I want to relabel these to actual physical values."

Thank you for clarifying.

In that case, specify the x and y vectors/matrices in the call to surf. Something like

surf(t,x,u)

or

surf(x,t,u)

depending on the orientation of u with respect to t and x.

[Mat Hunt]

Don't I need to use meshgrid or something?

[Voss]

Not necessarily. In surf(X,Y,Z) X and Y can be vectors or matrices.

meshgrid would be useful for constructing matrix X and Y from vector X and Y, but you can use the vectors directly in surf.

[Voss]

"Currently the axis values just represent the number of data points, so I want to change that to actual values of interest."

Specify the values of interest in the call to surf.

Example:

% 10 t values ranging from 0.01 to 0.02
t = linspace(0.01,0.02,10)

t = 1×10

0.0100 0.0111 0.0122 0.0133 0.0144 0.0156 0.0167 0.0178 0.0189 0.0200

% 15 x values ranging from 100 to 200
x = linspace(100,200,15)

x = 1×15

100.0000 107.1429 114.2857 121.4286 128.5714 135.7143 142.8571 150.0000 157.1429 164.2857 171.4286 178.5714 185.7143 192.8571 200.0000

% 15-by-10 matrix u
u = exp(t.*x.')

u = 15×10

2.7183 3.0377 3.3947 3.7937 4.2395 4.7377 5.2945 5.9167 6.6120 7.3891 2.9195 3.2886 3.7044 4.1727 4.7003 5.2945 5.9638 6.7178 7.5671 8.5238 3.1357 3.5603 4.0423 4.5897 5.2111 5.9167 6.7178 7.6274 8.6601 9.8327 3.3679 3.8544 4.4111 5.0483 5.7775 6.6120 7.5671 8.6601 9.9111 11.3427 3.6173 4.1727 4.8135 5.5527 6.4054 7.3891 8.5238 9.8327 11.3427 13.0845 3.8851 4.5174 5.2526 6.1075 7.1016 8.2574 9.6014 11.1640 12.9811 15.0938 4.1727 4.8905 5.7318 6.7178 7.8734 9.2278 10.8152 12.6756 14.8561 17.4117 4.4817 5.2945 6.2547 7.3891 8.7291 10.3123 12.1825 14.3919 17.0020 20.0855 4.8135 5.7318 6.8253 8.1274 9.6779 11.5241 13.7226 16.3406 19.4579 23.1700 5.1699 6.2053 7.4479 8.9395 10.7297 12.8785 15.4575 18.5531 22.2685 26.7281

% plot the surface
surf(t,x,u)
xlabel('t')
ylabel('x')
zlabel('u')

Answer 2

[Sufiyan]

I believe this is similar to changing the limits on the axis scale to different values or rescaling the axis.

you can refer to https://in.mathworks.com/matlabcentral/answers/459421-changing-the-scale-of-axis-in-surf-plot

[Mat Hunt]

This isn't the problem I have.