Look like you want to select exactly 1 element per row, from among all columns of the matrix. Hence, if there are m rows and n elements per row (or n columns), there would be n^m combinations generated (2^3 = 8 in your question).
Solution using combvec()
Please read up on combvec here:
If we give row vectors as inputs to combvec(), it generates all possible combinations of elements from those row vectors. Hence, we may pass each row to combvec() as a separate argument, as illustrated below:
mat = [1 2; 1 2; 1 2];
ans = combvec(mat(1,:), mat(2,:), mat(3,:))
If the number of rows is not known, you may want to use a for loop:
num_rows = size(mat,1);
combs = mat(1,:);
combs = combvec(mat(i,:), combs);
Hope it Helps!