imy e</code> returns a two-dimensional array
   (an array of arrays) with first dimension <code class="code">dimx</code> and
   second dimension <code class="code">dimy</code>. All the elements of this new matrix
   are initially physically equal to <code class="code">e</code>.
   The element (<code class="code">x,y</code>) of a matrix <code class="code">m</code> is accessed
   with the notation <code class="code">m.(x).(y)</code>.
<p>

   Raise <code class="code"><span class="constructor">Invalid_argument<