To write data to a text file in MATLAB, you can use the fprintf function. Here is an example of how to use it: 

% Open the file for writing
fileID = fopen('myfile.txt', 'w');

% Write data to the file
fprintf(fileID, '%s\n', 'Hello, world!');
fprintf(fileID, '%d %d\n', [1, 2; 3, 4]);

% Close the file
fclose(fileID);

In this example, myfile.txt is the name of the file you want to write to, and 'w' specifies that you want to open the file for writing (and overwrite any existing file with the same name).

The first fprintf call writes the string 'Hello, world!' to the file, followed by a newline character (\n). The second fprintf call writes a 2x2 matrix to the file, using the format specifier %d to indicate that the values should be written as integers.

After writing to the file, you should always close it using the fclose function to ensure that all data is properly written and that the file is released from memory.