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