If a matrix A has n rows and n columns then we say it's a square matrix.
A diagonal matrix is a square matrix with all de non-diagonal elements 0. The diagonal matrix is completely denoted by the diagonal elements.
The matrix is denoted by diag(1 , 5 , 9)
A matrix with one row is called a row matrix
A matrix with one column is called a column matrix
Matrix A and B are of the same kind if A has as many rows as B and A has as many columns as B
The n x m matrix AT is the transpose of the m x n matrix A if and only if The ith row of A = the ith column of A' for (i = 1,2,3,..n).
When all the elements of a matrix A are 0, we call A a 0-matrix.
An identity matrix I is a diagonal matrix with all diagonal element = 1
If we change the sign of all the elements of a matrix A, we have the opposite matrix -A.
A square matrix is called symmetric if it is equal to its transpose.