symm returns the symmetric part of the argument matrix. This is
the nearest symmetric (Hermitian) matrix to the argument in both the
Frobenius norm and 2-norm.
This is not an built-in function. This function
is normally loaded on start-up from the symm.r file in the
standard rlib directory. Use of the -r option, incorrectly
setting the RLAB_LIB_DIR environmental variable, or modifying
symm.r may make this function unavailable.