Matrix times Column Matrix

Here is an example of a matrix times a column matrix:

The details of how this is done will be explained later. For now, look at the dimensions of the operands and of the result. A matrix times column matrix product can be formed if the dimensions look like this:

Matrix  x  Col. Matrix   =   Resulting Col. Matrix

R x N      N x 1         =         R x 1
    --------
      same

For the above example:

Matrix  x  Col. Matrix   =   Resulting Col. Matrix

2 x 2      2 x 1         =         2 x 1
    --------
      same

Dimensions are displayed as "Row x Column". An R x 1 matrix is a column matrix (because it has 1 column).