How to save matlab coding output data in a file?

Hello,

I am working with matlab coding. I need to run the simulations for different models. For the 1st model, I run the simulation, it saves output in the workspace. but when i run the 2nd model, it saves the output file for the 2nd model. That is why i need to save the output for the 1st model to a file. So, i can store my outputs of all models.

can anyone please suggest me how to do?

[Stephen23]

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

https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html

[Walter Roberson]

is this a Simulink question ?

[madhan ravi]

If you are talking about simulink look into simout block.

[Sky Scrapper]

no, not simulink. it's matlab coding file using matlab editor.

say for the 1st model, I have data saved on workspace:

output= 100x10 matrix

P= 22x1 matrix

Q= 7x1 matrix.

For the model 2, i have,

output= 230x8 matrix

P= 12x1 matrix

Q= 7x1 matrix.

If I run the second model, then I will lost all the data for the 1st model saved on the matlab workspace window. That why I want to save the data of the 1st model to a file so that I will get all the data while I am working with another model.

[madhan ravi]

https://www.mathworks.com/matlabcentral/answers/443879-how-to-save-matlab-coding-output-data-in-a-file#comment_669051

[Sky Scrapper]

sorry, your link is not working.

[madhan ravi]

Why not use save() ?

[Sky Scrapper]

My file name is: for 1st model: final output

for 2nd model: output

I am writing:

save (' finaloutput.mat',' output','P')

it is working but i do not know where it is saving.

[madhan ravi]

It saves in a file named finaloutput.mat to use the values simply use

load finaloutput.mat % variables will be loaded in workspace

[Sky Scrapper]

it's showing error:

''Error using load

Number of columns on line 3 of ASCII file finaloutput.m must be the same as previous lines.''

[Walter Roberson]

Do not save naming .m file as destination . Name a .mat file.

Answer 1

[Omer Yasin Birey]

You can save them in matfiles

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

[Sky Scrapper]

If I am writing:

m = matfile('finaloutput.m','Writable',true);

it's showing:

Error using matlab.internal.language.isPartialMATArrayAccessEfficient

Unable to read MAT-file C:\Users\\Desktop\finaloutput.m: not a binary MAT-file.

[Omer Yasin Birey]

Hi, you should have written 'finaloutput.mat' not 'finaloutput.m'. Try this

  m = matfile('finaloutput.mat','Writable',true);% now you will use m to save
  m.oldVariable = variableThatYouWantToSave; %its the variable that you want to save  

and after your new simulation you can add the new variable into this matfile

  m.newVariable = newVariableThatYouWantToSave;%new variable

[Sky Scrapper]

yes that is working. if i want to save the data stored in more than one variable say 'p' 'q'

then, m.oldVariable = 'p','q'

but it will not work.

then how to do?

[Omer Yasin Birey]

save('finaloutput.mat','p','q','-append')

Don't forget to write '-append' at the end otherwise it will write the variables over your existing variables. Meaning that your old variables will be deleted.

[Sky Scrapper]

it I use directly: save('finaloutput.mat','p','q','-append')

then where the file will be saved? i mean it does not show on the workspace.Then where to find the saved file?

[Omer Yasin Birey]

load('finaloutput.mat')

This line above will bring you the old variable.

About the directory, the mat file will be in the folder that you work in. When you write the line above, the variables will appear in the workspace.

[Sky Scrapper]

while i am using:

save('finaloutput.mat','p','q','-append')

it is showing error that 'q' has not is not a valid variable name.

[Omer Yasin Birey]

That has to be something else, q is a valid variable name. Maybe, you are missing an apostrophe between the commas or something.

[Sky Scrapper]

nope. i have just copied from here. is it possible to do with:

m = matfile('finaloutput.mat','Writable',true);

m.oldVariable = variableThatYouWantToSave;

this or i need to write:

m.oldVariable = variableThatYouWantToSave;

seperately for each variable?

[Omer Yasin Birey]

To use matfile object, m, you have to write this line for each variable

m.oldVariable = variableThatYouWantToSave; 
m.newVariable = new;% etc

But it is strange that 'q' is giving that kind of error.

[Sky Scrapper]

it's ok. could you please let me know how to delete one variable once stored. say, i want to delete the data of 'q' variable now?

[Omer Yasin Birey]

Unfortunately, matfiles doesn't have remove option. But at this link the user wrote a function for this. You can use it by copying the .m file into your folder. It seems working

https://www.mathworks.com/matlabcentral/fileexchange/19384-rmvar-remove-variables-from-mat-file

[Sky Scrapper]

ok thanks a lot.

[Stephen23]

"Don't forget to write '-append' at the end otherwise it will write the variables over your existing variables. Meaning that your old variables will be deleted."

Yet that is exactly what the -append option does for .mat files: it overwrites existing variables of the same name, which confuses a lot of beginners (it would be better named overwrite or something similar). This is explained in the save help (and easily checked with a few tests).

The suggested answer to use matfile is pointlessly complex for this trivial task. Much simpler to use save in a loop, generating the filename each time:

https://www.mathworks.com/matlabcentral/answers/443879-how-to-save-matlab-coding-output-data-in-a-file#comment_669051

https://www.mathworks.com/matlabcentral/answers/443879-how-to-save-matlab-coding-output-data-in-a-file#comment_669067