symmetric matrices containing exactly ones and zeroes exist?
How many
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A symmetric matrix would have A T = A . Note that in the transpose matrix, the diagonal elements remain where they are and other elements get 'mirrored' along the diagonal.If we divide the board into 3 parts, the diagonal, the lower half and the upper half, every arrangement of the lower half will have only one arrangement in the upper half such that A T = A . For this reason, there cannot be an odd number of 1 ′ s outside the diagonal (lower + upper half). Each half has 2 8 blocks and the diagonal has 8 blocks. Therefore in total, there would be ( 4 2 8 ) ( 1 8 ) + ( 3 2 8 ) ( 3 8 ) + ( 2 2 8 ) ( 5 8 ) + ( 1 2 8 ) ( 7 8 ) = 3 6 8 6 4 8 matrices