Find sub-matrix containing the maximum number of elements consisting only of 1's

Question

I am trying to get help on it here, originally posted first at:

https://stackoverflow.com/questions/59446920/find-sub-matrix-containing-the-maximum-number-of-elements-consisting-only-of-1s

Basically trying to get the max sub matrix that contains only 1's of a matrix that is filled with 0's and 1's.

I could figure out the max sub matrix, now I just need to find how to do so that the sub matrix is only 1's.