Thread: calculate matrices

Please help, I searched the text several times but could not figure out how to solve this problem

How many 6 x 6 (0, 1)-matrices A are there with A = A^tr?

Maybe you can find first how many symmetric 2 x 2 and 3 x 3 (0, 1)-matrices there are.

Originally Posted by wattskickin

Please help, I searched the text several times but could not figure out how to solve this problem

How many 6 x 6 (0, 1)-matrices A are there with A =A^tr?

I hope this is what you mean.
How many 6x6 matrices can be there such that . Elements of the matrices can be selected from the set ?

Sol: For we need where is the element in the row column.
We consider the elements where (why ?). There are 21 such elements and for each of these elements we have 2 choices so we have such matrices.

Kalyan.