Function: matrix
Section: linear_algebra
C-Name: matrice
Prototype: GDGDVDVDE
Help: matrix(m,{n=m},{X},{Y},{expr=0}): m x n matrix of expression expr,
 where the row variable X goes from 1 to m and the column variable Y goes from
 1 to n. By default, fill with 0s.
Doc: creation of the
 $m\times n$ matrix whose coefficients are given by the expression
 \var{expr}. There are two formal parameters in \var{expr}, the first one
 ($X$) corresponding to the rows, the second ($Y$) to the columns, and $X$
 goes from 1 to $m$, $Y$ goes from 1 to $n$. If one of the last 3 parameters
 is omitted, fill the matrix with zeroes. If $n$ is omitted, return a
 square $m \times m$ matrix.
 %\syn{NO}
