How to read and write a matrix in/from a file on MATLAB?

Let's we assume that, I have a matrix :

 %A=[M,N];
 A=[ 5 5 5 5 5 55  5 55 5 ]

, I want to save A in a file TXT. and I can't open that file another time. Also I can modify that file, for example A=A*5;

I did not find the code.

Answer 1

[Image Analyst]

Why can't you open it at another time? How did you write it? Did you use writematrix() or csvwrite()? Or did you use fprintf() but forgot to call fclose():

fid = fopen('TXT.txt', 'wt');
fprintf(fid, '%d ', A);
fclose(fid);  % You need this, otherwise MATLAB MAY have a lock on it and other programs won't be able to open it.