How do I plot a 3D surface where I have arrays x and y of same length and z values for each x and y value.

So my code looks like the following

for n = 1:640; %number of time steps
    for q = 1:640; %number of axial increments on a tool
        Find a certain force f(q) = ...; % find force for each q increment
        K = 100
        z(n,q) = f(q)/K;
    end
end

Now at the end I want to generate a surface where there is a z value for every q and every n combination. So z is a (n x q) size matrix. So I want 640 time steps as x. 640 axial increments as y, and a z value for each x and y combination. So the z matrix has 640*640 size

Answer 1

[Cris LaPierre]

Read the documentation for surf.

[Mirwais Sharifi]

Hi Cris,

I have read the surf documentation and implemented the following changes, but i still get an error saying Z must be a matrix, not a scalar or vector. What should I do to fix this?

for n = 1:640; %number of time steps
    for q = 1:640; %number of axial increments on a tool
        Find a certain force f(q) = ...; % find force for each q increment
        K = 100
        [X,Y] = meshgrid(1:0.0000625:0.04, 1:0.0079375:5.08) % making x and y increment 640 times
        Z(n,q) = f(q)/K;
        hold on
        surf(X,Y,Z)
    end
end

[Mirwais Sharifi]

Sorry, I mean to write [X,Y] = meshgrid(0:0.0000625;0.04, 0:0.0079375:5.08), to ensure both x and y to increment 640 times

[Cris LaPierre]

If you are running the same code you are posting, Z is a nxq matrix (although what is shown will only throw errors).

You should organize your code a little better. If you choose to use meshgrid (and you don't have to), you only need to do so once. The same with the surf command. You are creating X and Y and plotting the surface 640x640 times

[Mirwais Sharifi]

That is not the complete code as the code is 200 lines. That is just the general logic behind what Im trying to do.

I have deleted the meshgrid and used the surf outside both for loops and get the error as data dimensions must agree.

So just to clarify what I'm trying to do:

I have 640 time increments (for n =1:640)

within each time increment I have 640 axial increments ( q = 1:640)

Now for each time increment and each of the 640 increments for the single increment I have a z value. z is (n x q) sized.

Fininally for each time increment ill have 640 z values. And same for next time increment (640 z values) until 640 time increments have completed and I'll have a total of 640x640 z values.

I am trying to plot the z values found for the corresponding n and q values in the for loop.

The surf documentation does not explain how to do this and says that x,y,z have to be matrices of the same size and I have no idea of going about this.

Thanks for your help Cris

[Cris LaPierre]

The hypothetical code is creating variables with the correct size. What is the size of the variables created in your actual code? Put a breakpoint in at the surf command and see what the actual size of n, q and z are.

And to clarify, the documentation does not say that X, Y, and Z have to be matrices. X and Y can be matrices or vectors. Z in the only one that has to be a matrix. As a simple example, see below:

n=1:40;
q=1:60;
z = n'*q;
surf(n,q,z')