Understanding the given lines of code

Hello all, I am trying to understand the meaning of following lines of code, but not getting it clearly.

file_x_train = strcat( file_px, num2str(ii),'_M',num2str(M), '_N',num2str(N),'_', num2str(SNRdB),'dB.mat' );
file_h_train = strcat( file_py, num2str(ii),'_M',num2str(M), '_N',num2str(N),'_', num2str(SNRdB),'dB.mat' );
m1=matfile( file_x_train,'writable',true );
m1.x_subtrain =data_SNR_train;

where, M = number of antennas, N = number of elements, SNRdB is a constant value say 10 decibels.

I understood that first and second line of code is related to filename for a MAT file.

But I am not getting what does third and fourth line of code indicates.

Any help in this regard will be highly appreciated.

Answer 1

[Cris LaPierre]

Have you tried asking in MathWorks AI Chat Playground?

https://www.mathworks.com/matlabcentral/playground/new

After providing it your code and description, I asked it to provide a comment for each line. Here are the results

% Create file names based on ii, M, N, and SNRdB
file_x_train = strcat( file_px, num2str(ii),'_M',num2str(M), '_N',num2str(N),'_', num2str(SNRdB),'dB.mat' );
file_h_train = strcat( file_py, num2str(ii),'_M',num2str(M), '_N',num2str(N),'_', num2str(SNRdB),'dB.mat' );

% Create a matfile object with write access using the file name from above
m1=matfile( file_x_train,'writable',true );

% Assign the variable data_SNR_train to the x_subtrain property of the matfile object
m1.x_subtrain = data_SNR_train;

[chaaru datta]

Thank u sir for ur reply... I had asked question there also... But I am not getting from where x_subtrain is coming ?

[chaaru datta]

Ok sir....But I am having query regarding "x_subtrain"....I am not getting how matfile object have "x_subtrain" property?

[Cris LaPierre]

That is the name of a variable that exists in the mat file specificed by file_x_train.

You can read more here: https://www.mathworks.com/help/matlab/ref/matlab.io.matfile.html

To clarify, this code doesn't create the mat file. It uses code to dynamically specify which existing matfile to access and change. The variable m1 is an object the code uses to access the specified mat file.

[Cris LaPierre]

If you are unfamiliar with mat files, then this page on how to create them may be helpful

https://www.mathworks.com/help/matlab/ref/save.html

[Aquatris]

When you load a matfile using the matfile function, you create a structure and assigns each variable of the mat file to a field in the structure.

Then with the code:

m1.x_subtrain = data_SNR_train;

you just add another field to your structure, just like what the comment says.

From your recent questions it feels like you are new to Matlab and also coding, so I recommend going through the basics of Matlab programming.

[Cris LaPierre]

Just a clarification that matfile does not load the matfile. From the matfile doc page (emphasis added)

• "Use a MAT-file object to access and change variables in a MAT-file without loading the file into memory."

[chaaru datta]

@Cris LaPierre, @Aquatris Thank u sir for ur response...

[Aquatris]

Yes I should not have used load in my explanation. Thank you for the correction