Array operations- vectorization. Error with matrix dimensions.

Hi! Sorry if it's stupid question, but I'm newbie with MATLAB. I wanted to use vectorization in my function which applies forward mapping (affine transformation of 2D image). I found vectorization in MATLAB documentation https://www.mathworks.com/help/matlab/matlab_prog/vectorization.html?requestedDomain=true#btjk57v-1 . The problem is I wanted to try the example stated there under the topic of array operations.

x = (-2:0.2:2)'; % 21-by-1
y = -1.5:0.2:1.5; % 1-by-16
F = x.*exp(-x.^2-y.^2); % 21-by-16

And the error appeared: Error using - Matrix dimensions must agree. What can be a problem here? It is example from documentation, so I'm kinda confused why it is not working for me.

Answer 1

[Guillaume]

The problem is simple, you're looking at the most recent documentation but you're using an old version of matlab, earlier than R2016b.

From matlab's command prompt type

web(fullfile(docroot, 'matlab/matlab_prog/vectorization.html'))

to see the documentation that apply to your version.

R2016b introduced implicit expansion, in earlier versions you have to use bsxfun to do the same. The example code would have to be:

x = (-2:0.2:2)'; % 21-by-1
y = -1.5:0.2:1.5; % 1-by-16
F = bsxfun(@times, x, exp(bsxfun(@plus, -x.^2, -y.^2)))

[Kamil Galazka]

Yea, I supposed that this can be the problem with my version of MATLAB (2015b from the moment I bought it). I kept forgetting to update it. So far I didn't have any problems. I'll try both meshgrid and bsxfun and check the results. Thanks for clarification :)

[Guillaume]

Using bsxfun should be faster and definitively will use less memory than meshgrid. bsxfun is the direct ancestor of the implicit expansion that is used in the example.

Answer 2

[Torsten]

https://de.mathworks.com/help/matlab/ref/meshgrid.html

Best wishes

Torsten.

[Kamil Galazka]

Thank you very much. All clear now :)

Best wishes!