|  |  4.13.2 matrix expressions 
A matrix expression is:
 
an identifier of type matrix
a function returning matrix
matrix expressions combined by the arithmetic operations
+,-or*
a type cast to matrix (see  matrix type cast)
 
Example:
 |  |   ring r=0,(x,y),dp;
  poly f= x3y2 + 2x2y2 +2;
  matrix H = jacob(jacob(f));    // the Hessian of f
  matrix mc = coef(f,y);
  print(mc);
==> y2,    1,
==> x3+2x2,2 
  module MD = [x+y,1,x],[x+y,0,y];
  matrix M = MD;
  print(M);
==> x+y,x+y,
==> 1,  0,  
==> x,  y   
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