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  ×  Col. Matrix   =   Resulting Col. Matrix

R × N      N × 1         =         R × 1
    --------
      same

For the above example:

Matrix  ×  Col. Matrix   =   Resulting Col. Matrix

2 × 2      2 × 1         =         2 × 1
    --------
      same

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