__Matrix__

Matrix is a rectangular arrangement of numbers, arranged in horizontal rows and vertical columns. Plural of matrix is matrices. e.g.

, ,

Note:

- Each entity or number in a matrix is called an element.
- In any matrix Horizontal lines are called rows while the vertical lines are called columns.

__Order of Matrix__

If a matrix has columns and rows, then the order is written as .

So for example in , . Hence .

Matrices are normally denoted by capital letters. If is a matrix with rows and columns, then it is denoted as .

__Elements of a Matrix__

Each entity or number in a matrix is called an element.

If is a matrix with rows and columns, then the number of elements would be .

__Types of Matrices__

*Row Matrix*: This is a matrix, that has only one row. e.g.

*Column Matrix*: This is a matrix, that has only one column. e.g.

*Square Matrix*: This is a matrix where the number of rows are equal to number of columns. e.g.

*Rectangular Matrix*: This is a matrix where the number of rows are not equal to number of columns. e.g.

*Zero or Null Matrix*: If each element of a matrix is 0, then it is called Zero or Null Matrix. e.g. , ,

*Diagonal Matrix*: This is a square matrix, where all elements are 0 except the ones on the leading diagonal. e.g.

*Unit or Identity Matrix*: A diagonal matrix, where each element of the leading diagonal is 1 is called Unit or Identity matrix. e.g. ,

__Transpose a Matrix__

Transpose of a matrix is obtained by interchanging its rows and columns. Transpose of a matrix . e.g:

If , then

__Equality of Matrices__

Two matrices A and B are said to be equal if:

- The matrices have the same order
- the corresponding elements of the two matrices are the same.

e.g. If , and , then

__Addition of Matrix__

Two matrices can be added only if the order of the two matrices is the same. To add two matrices of the same order, just add the corresponding terms. e.g.

__Subtraction of Matrix__

Two matrices can be subtracted only if the order of the two matrices is the same. To subtract two matrices of the same order, just subtract the corresponding terms. e.g.

Note: If are matrices of the same order, then:

- (addition of matrices is commutative)
- (addition of matrices is associative)

__Additive Identity of a Matrix__

0 is called the additive identity of any number because the number does not change. Similarly, there is an additive identity of a matrix as well.

If a matrix is added to a null matrix of the same order, the matrix remains unchanged. Hence the null matrix of the same order is called the Additive Identity of the matrix. e.g.

__Additive Inverse of a Matrix__

If are two matrices of the same order such that matrix, then is called the additive inverse of and is called the additive inverse of . Additive inverse of (just multiply by ). e.g.

If , then which is the additive inverse of A.

__Multiplication of Matrix by a scalar (real number)__

__Case 1:__

To multiply a matrix by a scalar, just multiply each of the element of the matrix by the scalar. e.g.

__Case 2:__

Multiplication of two matrices: Two matrices A and B can be multiplied to each other only if the number of columns in A is equal to the number of rows in B. e.g.

Let and

Number of columns in A = 2 which is equal to the number of rows in B=2. Hence we can multiply these matrices.

__Identity Matrix for Multiplication__

If is any matrix, then the identity matrix of (unit matrix of the same order as that of ). In that case,

Let

Then

*Note: If the order of matrix and the order of matrix , then the product is possible (because ). If is the product matrix, then the order of matrix .*

Note:

- For any three matrices , which are compatible for multiplication, . Similarly i.e. product of matrices is associative.
- Normally unless . Multiplication of matrices is not commutative.
- If then it is not necessary that
- If , then it is not necessary that
- If , then
- i.e. multiplication is distributive over addition i matrices. In the same way