Function: mathnfmodid
Section: linear_algebra
C-Name: hnfmodid
Prototype: GG
Help: mathnfmodid(x,d): (upper triangular) Hermite normal form of x
 concatenated with d times the identity matrix.
Doc: outputs the (upper triangular)
 \idx{Hermite normal form} of $x$ concatenated with $d$ times
 the identity matrix. Assumes that $x$ has integer entries.
