Comparing binary matrices and weights

271 Views Asked by At

If two $n×m$ binary matrices have the same row weights, column weights, upper-diagonal weights and lower-diagonal weights, are they necessarily identical?

The weight of a given row, column, or diagonal is the number of entries with $1$ in that row, column, or diagonal.

The following matrix:$$ \begin{pmatrix} 1 & 0 & 1\\ 0 & 1 & 1\\ 1 & 1 & 0 \end{pmatrix} $$ has the row, column, and diagonal weights:

Row: $2, 2, 2$

Col: $2, 2, 2$

Upper diagonal: $1, 0, 3, 2, 0$

Lower diagonal: $1, 1, 2, 1, 1$

At first I considered only when the row and column weights are the same. I found a counter example. Then I considered only when the upper and lower diagonals weights. Yet again, I found a counter example.

How can one going about proving it? Or does anyone have a counter example? I have no been able to find one thus far.

1

There are 1 best solutions below

0
On BEST ANSWER

Take$$ A = \begin{pmatrix} 0 & 1 & 0 & 0\\ 0 & 0 & 0 & 1\\ 1 & 0 & 0 & 0\\ 0 & 0 & 1 & 0 \end{pmatrix}, \quad B = \begin{pmatrix} 0 & 0 & 1 & 0\\ 1 & 0 & 0 & 0\\ 0 & 0 & 0 & 1\\ 0 & 1 & 0 & 0 \end{pmatrix}. $$