You haven't provided enough detail to answer your question too specifically but in general the steps would be to read the individual data files into MATLAB and assign the data in each file to a matlab array. You could then perform the desired matrix addition on the elements of this matlab array. So for example:
% assign your dimensions
numRows = 300 % number of rows in your individual matrices
numCols = 19 % number of columns in your individual matrices
numMats = 240 % number of individual matrices
% preallocate array to hold the data
A = zeros(numRows,numCols,numMats);
% loop to read individual matrices from files
for k = 1:numMats
% build the name of the data file as a character vector'
filename = ['DOS',num2str(k)];
A(:,:,k) = readmatrix(filename);
end
% now for example add the first and third matrix
B = A(:,:,1) + A(:,:,3)
You may have to modify the above code to fit the specifics of your situation, but this should give you an idea of how it could be done.
