Matrix Square


1. Matrix multiplication is inner product of a row of **A **with a column of **A**T
2. But the columns of **A**T are the rows of **A**, so the entry corresponds to the inner product of tworows of **A** If *pij * is the entry of the product
3. So it is symmatric
$$A^2 = A^TA$$
[Symmetric Matrix](https://texonom.com/symmetric-matrix-8ab18b2c502545e08445c0110a090131) also
[Symmetric positive semi-definite](https://texonom.com/symmetric-positive-semi-definite-16ce5c2766e94f3d803ea6ddf2742660) 



> [Is a matrix multiplied with its transpose something special?](https://math.stackexchange.com/questions/158219/is-a-matrix-multiplied-with-its-transpose-something-special)





