Sum of N matrices

The reason for this new message was to request a new favor.

Is there a code or function in matlab that allows me to add an undefined number (N) of matrices, which I already have a program? As an example I put the following situation to be understood better:

Aux = Mat (1) + Mat (2) + Mat (3) + .... + Mat (n)

I thank you for your attention and I hope you can help me with my predicament.

[per isakson]

"undefined number (N) of matrices" How are the matrices stored?

Try this

>> N = 12;
>> M = ones(3,4,N);  % N 3x4 matrices
>> aux = sum( M, 3 )
aux =
    12    12    12    12
    12    12    12    12
    12    12    12    12
>>

[Stephen23]

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

[Pedro Guevara]

Thank you very much for your answer. Look, in these 4 lines of code I am generating and saving each of my N matrices (my matrixes generated with 6x6). I hope you can help me with this topic. Thank you.

   M_Kele_G=inv(M_Trans)*M_Kele*M_Trans;
   M_Kele_global =['MK_G',int2str(f),' = M_Kele_G'];
   eval(M_Kele_global)  
   eval(['MK_G', num2str(f)])

[Rik]

You should change the way you assign your data. Have you read the link Stephen gave you?

[Pedro Guevara]

Thanks for your answer. What happens is that I am a beginner in matlab and until recently I began to program in this software, I do not know many things about it. The program that I already started has been pretty much taken advantage of using the eval function and I do not want to lose all that work. If you could help me with the application without having to do it by indexing, I would greatly appreciate it.

[Matt J]

The program that I already started has been pretty much taken advantage of using the eval function and I do not want to lose all that work.

Why not? That work hasn't helped you. It has hurt you, and will continue to hurt you. I'm willing to bet money that whatever you did with eval can be remade in 1/10th the time using the better practices described at Stephen's link.

[Pedro Guevara]

OK, I will try to make my code implementing indexing. Could you ask for help if you need it? I appreciate your attention.

[Stephen23]

@Pedro Guevara: the approach using eval is specifically advised against by all experienced MATLAB users and by the MATLAB documentation, which has a whole page explaining why to avoid doing this. It states "A frequent use of the eval function is to create sets of variables such as A1, A2, ..., An, but this approach does not the array processing power of MATLAB and is not recommended. The preferred method is to store related data in a single array."

You have already already wasted more than one day trying to work with this inefficiently designed code, in contrast per isakson gave a much better solution in just a few seconds, which is simpler, neater, more efficient, less buggy, and easier to work with. This is one reason why you should rewrite your code: it will save you time! Do you see the pattern here? If you continue to design your code like this, then you will continue to fight your code for no real benefit. Or you could use arrays and indexing, which is what the MATLAB documentation recommends, and make developing, debugging, and running your code much faster.

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

Answer 1

[per isakson]

I've modified the example of my comment.

n   = 12;
sz  = [3,3];
MKG = nan( sz(1),sz(2), n );
for ix = 1 : n
    MKG(:,:,ix) = ones(sz); % inv(M_Trans)*M_Kele*M_Trans;
end
sum( MKG, 3 )

outputs

ans =
    12    12    12
    12    12    12
    12    12    12
>>

[Pedro Guevara]

I think I love you. XD I am trying to understand your code by making it run step by step and apparently, with some modifications, you can help me with the purpose of my work. Thank you very much.