How to store a matrix so that I can call upon it in any other file I am working in?

Hi there,

I am trying to save a matrix of data that I want to use, so that I can call upon it whenever I wish. Plus, I don't want it taking up space in my other script I am working on. I have been searching online how to do this apparent simple task, but can't seem to get it right.

So say I'm in a file called Frame2.mat, and the matrix is:

A = rand(10,10)

A = 10×10

0.5228 0.7856 0.3229 0.6056 0.3178 0.8621 0.8351 0.8522 0.6084 0.0708 0.8254 0.4739 0.8760 0.3915 0.5663 0.8099 0.1573 0.9719 0.3930 0.7211 0.9450 0.8130 0.5576 0.2800 0.4407 0.3070 0.9011 0.7068 0.2419 0.1356 0.0966 0.8290 0.4090 0.8699 0.8585 0.7259 0.0443 0.7975 0.6078 0.6212 0.0465 0.6980 0.5365 0.0164 0.0368 0.4520 0.2349 0.6107 0.2868 0.7108 0.1046 0.3271 0.5281 0.3637 0.6896 0.2049 0.8954 0.0560 0.8737 0.0928 0.0100 0.8795 0.2607 0.7931 0.8346 0.3888 0.2983 0.3102 0.1165 0.0741 0.6809 0.5309 0.9333 0.4969 0.9272 0.2590 0.7933 0.3678 0.9152 0.6260 0.6133 0.5114 0.2475 0.7920 0.0814 0.5666 0.4892 0.2776 0.3486 0.4589 0.8599 0.2761 0.4248 0.8110 0.2638 0.9842 0.6746 0.2426 0.4833 0.7074

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Then I go to another file I am working in and want to call upon matrix A and extract the first column.

So in this different file (not Frame2) I want to use:

T = A(:,1)

T = 10×1

0.5228 0.8254 0.9450 0.0966 0.0465 0.1046 0.0100 0.6809 0.6133 0.8599

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How do I do this?

Many thanks

Scott

[Stephen23]

"So say I'm in a file called Frame2.mat, and the matrix is: A = rand(10,10)"

Are you attempting to write a .mat file yourself as a text file? That does not make sense.

Answer 1

[Torsten]

Declare the matrix as "global" or pass it as input argument to all functions where it is needed.

Or save it as a .mat-file and load it where it is needed.

[John D'Errico]

So many ways. Another is to stuff it into an m-file function, that will return the desired matrix as its argument.

[Scott Banks]

I have tried saving it as:

save('Frame2.mat','A')

Then

load('Frame2.mat')

But this is working.

[Walter Roberson]

It is safer to use

A = load('Frame2.mat','A').A;

[Torsten]

You mean "But this is not working" ?

What error message do you get ?

Can you find a file with name "Frame2.mat" in your working directory after saving ?

[Scott Banks]

I just tried it again. This time using a file called "moment_frame2" and this happened after I tried to save my matrix.

[Torsten]

Works without problems for me:

A = [1 2;3 4];
save("Matrix.mat","A");
B = load("Matrix.mat","A").A;
B

B = 2×2

1 2 3 4

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[Walter Roberson]

Do not save your variable as a .m file, save it as a .mat file.

Or if you really want, save it as a .csv or .txt file that you then readmatrix at need, if you need the file to be editable.

You could also consider

function A = loadA()
  persistent A
  if isempty(A)
      A = load('Matrix.mat', 'A').A;
  end
end

after which you would call

A = loadA();

This had the advantage of only reading in A once and remembering the cached value the second and later times.

[Scott Banks]

Thanks, guys, I have it now!