# Main diagonal

In

linear algebra, the

**main diagonal** of a

square matrix is the diagonal which runs from the top left corner to the bottom right corner. For example, the following matrix has 1s down its main diagonal:

A matrix like the above in which

*only* the elements of the main diagonal are non-zero is called a

diagonal matrix. The sum of the entries on the main diagonal of a matrix is known as the

trace of that matrix.