Run the same code with multiple variables.

Hi!

I have 10-20 different matrices, each containing a set of coordinates (one longitude column & one latitude column). I wrote a code to calculate stuff for one matrix, but I want to loop the whole code for all of my matrices.

I need to compare the results from each matrix, so their results have to end up in a joint new matrix.

Thank you!

[Stephen23]

"I want to loop the whole code for all of my matrices"

Put the matrices into one array (which might be numeric or cell) and use indexing: indexing is simple, neat, easy to debug, and very efficient. The best solution would be to avoid this problem by using one array right from the very start, so that you can write simpler, more efficient code.

You should read this:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

It is possible to do what you asked for, but the MATLAB documentation states: "A frequent use of the eval function is to create sets of variables such as A1, A2, ..., An, but this approach does not use the array processing power of MATLAB and is not recommended. The preferred method is to store related data in a single array"

source: https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

[Hampus Alfredsson]

Thank you! I'm pretty new to Matlab, I believe an array is what I am looking for.

[Stephen23]

@Hampus Alfredsson: all numeric scalars/vectors/matrices are arrays in MATLAB, they are not a different class of variable (e.g. a scalar is just a 1x1x1x1x... array). The only thing is to use appropriate indexing:

https://www.mathworks.com/help/matlab/math/multidimensional-arrays.html

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html

[Hampus Alfredsson]

Ok! But also, my matrices are of different size but I still want to execute the code for each matrix. How can I store different sized matrices in a multidimensional array?

[Walter Roberson]

To store different sizes of matrices in a multidimensional array, you need to either concatenate them along a dimension that is known to be the same for each, or else you need to pad the smaller ones to be consistent size. Some of the common padding values are 0, nan, inf, and -9999

[Hampus Alfredsson]

Ok! I will look into this, thank you @Walter Robertson.

[Stephen23]

"How can I store different sized matrices in a multidimensional array?"

Or, as an alternative, use one simple cell array.

Answer 1

[Jeff Miller]

It might be convenient to store each of the 10-20 matrices as one cell in a cell array, since that doesn't require that they have the same size. Then, for each cell, call the code to process the one array in that cell.

[Jan]

Example:

% Create some test data:
C = cell(1, 20);
for k = 1:20
  n = randi([1,5], 1, 2);  % Some random dimensions
  C{k} = rand(n(1), n(2)); % A random matrix
end

% Now process them in a loop:
for k = 1:numel(C)
  C{k} = sin(C{k});
end