MATMUL (matrix-a, matrix-b)

  Class:  Transformational function - Generic

  Performs matrix multiplication of numeric or logical matrices.

  The "matrix"s can be arrays of rank one or two.  At least one
  argument must be rank two.  The size of the first (or only)
  dimension of "matrix-b" must equal the last (or only) dimension of
  "matrix-a".

  The type of the resulting array depends on the data types of the
  arguments.  The rank and shape of the result follows:

   o  If "matrix-a" has shape (n,m) and "matrix-b" has shape (m,k),
      the result is a rank-two array with shape (n,k).

   o  If "matrix-a" has shape (m) and "matrix-b" has shape (m,k), the
      result is a rank-one array with shape (k).

   o  If "matrix-a" has shape (n,m) and "matrix-b" has shape (m), the
      result is a rank-one array with shape (n).

  Examples:

  Consider the following:

  A is the matrix |2 3 4|, B is the matrix |2 3|,
                  |3 4 5|                  |3 4|
                                           |4 5|

  X is vector (1, 2), and Y is vector (1, 2, 3).

  The result of MATMUL (A, B) is the matrix-matrix product AB with
  the value

    |29 38|
    |38 50|

  The result of MATMUL (X, A) is the vector-matrix product XA with
  the value (8, 11, 14).

  The result of MATMUL (A, Y) is the matrix-vector product AY with
  the value (20, 26).