Function: matker
Section: linear_algebra
C-Name: matker0
Prototype: GD0,L,
Help: matker(x,{flag=0}): basis of the kernel of the matrix x. flag is
 optional, and may be set to 0: default; non-zero: x is known to have
 integral entries.
Description:
 (gen, ?0):vec           ker($1)
 (gen, 1):vec            ZM_ker($1)
 (gen, #small)           $"incorrect flag in matker"
 (gen, small):vec        matker0($1, $2)
Doc: gives a basis for the kernel of the matrix $x$ as columns of a matrix.
 The matrix can have entries of any type, provided they are compatible with
 the generic arithmetic operations ($+$, $\times$ and $/$).

 If $x$ is known to have integral entries, set $\fl=1$.

Variant: Also available are \fun{GEN}{ker}{GEN x} ($\fl=0$),
 \fun{GEN}{ZM_ker}{GEN x} ($\fl=1$).
