Matrices are often represented by capital roman letters such as formula_1, formula_2 and formula_3, and there are rules for adding, subtracting and "multiplying" matrices together, but the rules are different than for numbers. As an example, the product formula_4 does not always give the same result as formula_5, which is the case for the multiplication of ordinary numbers. A matrix can have more than 2 dimensions, such as a 3D matrix. Also, a matrix can be one-dimensional, as a single row or a single column.