Function: qfsign
Section: linear_algebra
C-Name: qfsign
Prototype: G
Help: qfsign(x): signature of the symmetric matrix x.
Doc:
 returns $[p,m]$ the signature of the quadratic form represented by the
 symmetric matrix $x$. Namely, $p$ (resp.~$m$) is the number of positive
 (resp.~negative) eigenvalues of $x$. The result is computed using Gaussian
 reduction.
