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MPSC Civil Engg.

Pre Exam – ENGINEERING MATHEMATICS Page | 1

ENGINEERING MATHEMATI CS :

Types of Matrices

1. Row Matrix:
A matrix having only one row is called as “Row Matrix or Row Vector”.
e.g. [1 2 1],[1 0 2 3 −3],[𝑎] etc.
2. Column Matrix :
A matrix having only one column is called as “Column Matrix or Column vector”.
1
1
e.g. :[2] ,[ ] ,[𝑏] etc.
−1
3
Note that : A row or column matrix is also called as vector.
3. Null or Zero Matrix:
A matrix containing only zeroes is called as “Null or Zero Matrix”.
0 0 0 [0]
e.g. [ ] ,[ ] , etc.
0 0 0
4. Square Matrix:
A matrix is said to be “Square Matrix”, if number of rows is equal to number of
column in it.
3 0 2
1 0
[ ] , [0 1 0] , [4]1×1 etc.
0 1 2×2
2 0 3 3×3
5. Diagonal Matrix:
A square matrix is said to be “Diagonal Matrix”, if all its non-diagonal entries are zero
and atleast one diagonal element are non zero.
1 0 0
1 0
e.g. [ ] , [0 0 0] , 𝑒𝑡𝑐
0 5
0 0 2
6. Scalar Matrix :
A diagonal matrix in which all entries on principal diagonal are equal is called as
“Scalar Matrix”.
2 0 0
4 0
e.g. : e.g. [ ] , [0 2 0] , 𝑒𝑡𝑐
0 4
0 0 2
7. Unit Matrix or Identity Matrix:
A scalar matrix in which all entries on principal diagonal are unit (one) is called as
“Unit or Identity Matrix”.
1 𝑖𝑓 𝑖 = 𝑗
i.e., [𝑎𝑖𝑗 ] is a Identity, if 𝑎𝑖𝑗 ={
0 𝑖𝑓 𝑖 ≠ 𝑗

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1 0 0
1 0
e.g. [ ] , [0 1 0] etc
0 1
0 0 1
8. Upper Triangular Matrix:
A matrix in which all entries below principal diagonal are zero is called as “Upper
triangular matrix”.
i.e., [𝑎𝑖𝑗 ] is a upper triangular, iff 𝑎𝑖𝑗 = 0 𝑖𝑓 𝑖 > 𝑗
1 2 3
1 2
e.g. :[ ] , [0 4 5] etc.
0 3
0 0 6

9. Lower Triangular Matrix:


A matrix in which all entries above principal diagonal are zero is called as “Lower
triangular matrix”.
i.e., [𝑎𝑖𝑗 ] is a lower triangular, iff 𝑎𝑖𝑗 = 0 𝑖𝑓 𝑖 < 𝑗
• Transpose of Matrix: The matrix obtained by inter changing rows in to column (or
column in to rows), is called as transpose of given matrix. If A is given matrix then
it’s transpose is denoted by 𝐴𝑇 (𝑜𝑟 𝐴𝑡 𝑜𝑟 𝐴′).
i.e., If A = [𝑎𝑖𝑗 ] then 𝐴𝑇 = [𝑎𝑖𝑗 ]
𝑎 𝑏 𝑎 𝑐
e.g. : If A =[ ], then 𝐴𝑇 = [ ]
𝑐 𝑑 𝑏 𝑑
• Real Matrix : Any matrix with all its entries as a real numbers is called as “Real
matrix”
• Complex Matrix : Any matrix with its entries as a complex numbers is called as
“Complex matrix”
10. Symmetric Matrix :
A square matrix A is said to be “Symmetric Matrix”
if = 𝐴𝑇 . i.e., If A is symmetric then A = [𝑎𝑖𝑗 ] = [𝑎𝑗𝑖 ] = 𝐴𝑇
𝑎 ℎ 𝑔
e. g. 𝐴 = [ℎ 𝑏 𝑓 ] , 𝐵 = [2 3
] = 𝐵𝑇 , etc.
3 4
𝑔 𝑓 𝑐

11. Skew-symmetric Matrix:


A square matrix A is said to be “Skew-symmetric Matrix”,
if = − 𝐴𝑇 . i.e., If A is skew-symmetric then A = [𝑎𝑖𝑗 ] = [𝑎𝑗𝑖 ] = −𝐴𝑇
0 1 2
0 −𝑎
e. g. 𝐴 = [−1 0 3] , 𝐵 = [ ], etc.
𝑎 0
−2 −3 0
Note that :
• In a skew-symmetric matrices all diagonal entries are always zero.
Since, for diagonal entries 𝑎𝑖𝑖 = −𝑎𝑖𝑖 which is possible only if 𝑎𝑖𝑖 = 0

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• If A is any square matrix, 𝐴 + 𝐴𝑇 is always symmetric while 𝐴 − 𝐴𝑇 is always skew-


𝐴+𝐴𝑇 𝐴−𝐴𝑇
symmetric, moreover we can write 𝐴 = 2
+ 2
. i.e., any square matrix can
be represented into the sum of symmetric and skew-symmetric matrices.
12. Orthogonal Matrix
A square matrix A is said to be “Orthogonal Matrix”,
if 𝐴 𝐴𝑇 = I = 𝐴𝑇 A or 𝐴𝑇 = 𝐴−1
Note That:
(a) If A is an Orthogonal Matrix then, 𝐴−1 =𝐴𝑇 .
(b) If A is an Orthogonal Matrix then, = |𝐴| = ± 1 .
(c) If A and B are an Orthogonal Matrices then, A, 𝐴−1 , 𝐴𝑇 and AB are also
Orthogonal.
(d)If A is real matrix, then (𝑖) A is orthogonal, (𝑖𝑖) the rows of A forms an orthonormal
set and (𝑖𝑖𝑖) the columns of A forms an orthonormal set, are equivalent.
(e) If A and B are symmetric matrices, then 𝐴 + 𝐵, 𝑘𝐴 (𝑓𝑜𝑟 𝑎𝑛𝑦 𝑠𝑐𝑎𝑙𝑎𝑟 𝑘), 𝐴2 , 𝐴𝑛 (𝑓𝑜𝑟 𝑛 >
0) are also symmetric
13. Hermitian matrix
A square complex matrix A is said to be “Hermitian Matrix”
̅̅̅̅
If 𝐴 = 𝐴𝐻 , where 𝐴𝐻 = (𝐴 𝑇 ) 𝑜𝑟 𝐴𝐻 = (𝐴̅)𝑇

0 1 + 2𝑖 2 − 3𝑖
𝑎 𝑐 + 𝑑𝑖
e. g. 𝐴 = [−1 + 2𝑖 0 3 + 4𝑖 ] = −𝐴𝐻 , 𝐵 = [ ] = 𝐵𝐻 , 𝑒𝑡𝑐.
𝑐 − 𝑑𝑖 𝑏
2 + 3𝑖 −3 + 4𝑖 0
14. Skew – herimition Matrix:
A square complex matrix A is said to be “Skew – Herimitian matrix”
If 𝐴 = −𝐴𝐻 , where 𝐴𝐻 = ̅̅̅̅
𝐴𝑇
0 1 + 2𝑖 2 − 3𝑖
𝑎 𝑐 + 𝑑𝑖
e. g. 𝐴 = [−1 + 2𝑖 0 3 + 4𝑖 ] = −𝐴𝐻 , 𝐵 = [ ( ] = −𝐵𝐻 , 𝑒𝑡𝑐.
− 𝑐 − 𝑑𝑖 ) 𝑏
−2 + 3𝑖 −3 + 4𝑖 0
Note that:
1. In a Hermitian matrices all diagonal entries are always Real.
2. In a skew-hermitian matrices all diagonal entries are always zero.
3. If matrix A is real matrix, then 𝐴𝑇 = 𝐴𝐻 .
4. If A is any complex square matrix, then 𝐴 + 𝐴𝐻 is always Herimitian and skew –
herimitian matrices.
15. Unitary Matrix :
A square complex matrix A is said to be “Unitary Matrix”,
if 𝐴 𝐴𝐻 = 𝐼 = 𝐴𝐻 𝐴 𝑜𝑟 𝐴𝐻 = 𝐴−1 .
Note that, (1) If A and B are unitary, then 𝐴𝐻 , 𝐴−1 . and AB are also unitary.
(2) If A is complex matrix, then (𝑖) A is unitary, (ii) the rows of A forms an orthonormal
set and

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(iii) the columns of A forms an orthonormal set, are equivalent.


16. Normal Matrix:
A square real (or Complex) matrix A is said to be “ Normal Matrix”, if its commutes
with 𝐴𝑇 (or 𝐴𝐻 ). i. e. 𝐴𝐴𝑇 = 𝐴𝑇 𝐴 ( 𝑜𝑟 𝐴𝐴𝐻 = 𝐴𝐻 𝐴)
2 1 2 1 2 −1 5 0
Ex: Let A = [ ] , then 𝐴 𝐴𝑇 = [ ][ ]=[ ]
−1 2 −1 2 −1 2 0 5
2 1 2 −1 5 0
and 𝐴𝑇 𝐴 = [ ][ ]=[ ]
−1 2 −1 2 0 5
Hence, A is Normal.
17. Singular matrix:
A square matrix A is said to be “ Singular matrix” , |𝐴| = 0.
2 1
e. g. The matrix A = [ ] is singular, since |𝐴| = 0
4 2
1 3 1
The matrix B = 0 1 0] is singular Since |𝐵| = 0
[
2 0 2
18. Non-singular Matrix :
A square matrix A is said to be “Non-singular Matrix”, if |𝐴| ≠ 0
2 1
e.g. : The matrix A = [ ] is non-singular, since |𝐴| ≠ 0
5 3
1 3 1
Similarly the matrix 𝐵 = [0 1 0]is non-singular.
2 0 4

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