Solution (source code)

= Solution

\b[True.] The <symmetric and antisymmetric parts of a matrix> are, in <Einstein summation convention>,
$$
S_{ij}=\frac{M_{ij}+M_{ji}}2,\qquad A_{ij}=\frac{M_{ij}-M_{ji}}2.
$$
They satisfy $S_{ji}=S_{ij}$, $A_{ji}=-A_{ij}$ and $S_{ij}+A_{ij}=M_{ij}$. This works over the real or complex numbers; it uses division by two.