FreeMat

- Main Page
- Related Pages

TIMES Matrix Multiply Operator

Section: Mathematical Operators

# Usage

Multiplies two numerical arrays. This operator is really a combination of three operators, all of which have the same general syntax:

      y = a * b

where `a` and `b` are arrays of numerical type. The result `y` depends on which of the following three situations applies to the arguments `a` and `b`:

1. `a` is a scalar, `b` is an arbitrary `n`-dimensional numerical array, in which case the output is the element-wise product of `b` with the scalar `a`.
2. `b` is a scalar, `a` is an arbitrary `n`-dimensional numerical array, in which case the output is the element-wise product of `a` with the scalar `b`.
3. `a,b` are conformant matrices, i.e., `a` is of size `M x K`, and `b` is of size `K x N`, in which case the output is of size `M x N` and is the matrix product of `a`, and `b`.

Matrix multiplication is only defined for matrices of type `double` and `single`.

# Internals

There are three formulae for the times operator. For the first form

and the second form

In the third form, the output is the matrix product of the arguments

# Examples

Here are some examples of using the matrix multiplication operator. First, the scalar examples (types 1 and 2 from the list above):

    --> a = [1,3,4;0,2,1]

    a =
     1 3 4
     0 2 1

    --> b = a * 2

    b =
     2 6 8
     0 4 2

The matrix form, where the first argument is `2 x 3`, and the second argument is `3 x 1`, so that the product is size `2 x 1`.

    --> a = [1,2,0;4,2,3]

    a =
     1 2 0
     4 2 3

    --> b = [5;3;1]

    b =
     5
     3
     1

    --> c = a*b

    c =
     11
     29

Note that the output is double precision.