Function: qfcholesky
Section: linear_algebra
C-Name: qfcholesky
Prototype: Gp
Help: qfcholesky(q): given a square symmetric matrix M, return R such that
 R~*R = M, or [] if there is no solution.
Doc: given a square symmetric \typ{MAT} $M$, return $R$ such that
 $^t{}R\*R = M$, or $[]$ if there is no solution.
