Lecture4

Lecture 4
Array addressing
Eng. Mohamed Awni
Electrical & Computer Engineering
Dept.

Agenda
2
 Vector addressing (linear address)
 Matrix addressing (Subscripts address).
 Colon (:) Operator in addressing arrays.
 Adding elements to existing arrays.
 Deleting elements of an existing arrays.
 Exercise & Homework

Vector Addressing (Linear address)
is its position in the arrayAddress of an element in an array
>> ve = [35 46 78 23 5 14 81 3 55]
ve =
35 46 78 23 5 14 81 3 55
1 2 3 4 5 6 7 8 9 position or index of element
ve(1) = 35
ve(2)= 46
.
.
.
.
ve(9)=55

Subscript Address • The address of an element in a matrix is
denoted by the row index and the column
index
• An element in the row number; i, and the
column number; j, of the matrix p is p (i, j)
• The address of an element in the first row
and the first column of the matrix is p(1,1)
not p(0, 0).
• The matrix indices begin from 1 (not 0 (as in C))
• The matrix indices must be positive integer
Matrix addressing (Subscript address)

4 10 1 6 2
8 1.2 9 4 25
7.2 5 7 1 11
0 0.5 4 5 56
23 83 13 0 10
1
2
Rows (m) 3
4
5
Columns
(n)
1 2 3 4 5
1 6 11 16 21
2 7 12 17 22
3 8 13 18 23
4 9 14 19 24
5 10 15 20 25
A = A (2,4)
A (17)
Matrix addressing

Colon (:) Operator in addressing arrays
Can be used to address a range of elements in a
vector or a matrix
A Colon (:)
Addressing a range of vector elements

7
4 10 1 6 2
8 1.2 9 4 25
7.2 5 7 1 11
0 0.5 4 5 56
23 83 13 0 10
1
2
3
4
5
1 2 3 4 5
1 6 11 16 21
2 7 12 17 22
3 8 13 18 23
4 9 14 19 24
5 10 15 20 25
A =
A(1:5,5)
A(:,5)
A(21:25)
A(4:5,1:2)
A([4 9;5 10])
Addressing a range of matrix elements
Colon (:) Operator in addressing arrays
A(:,n) Elements in all the rows of column “n” of the matrix A. (column)
A(n,:) Elements in all the columns of row “n” of the matrix A (row)
A(:,m:n) Elements in all the rows between columns m and n of matrix A
A(:,2:3) A(2,:)
A([2 7 12 17 22])
A(m:n,p:q) Elements in rows m through n and columns p through q of the
matrix A

Adding elements to existing arrays.
• An existing vector can be changed to have more elements
• An existing matrix can be changed to have more rows and/or columns
1 Adding elements to a vector
A = 98 23 12 11 231 2 3 4 5
>> A(6)=12;
>> A
A = 98 23 12 11 23 6
12
240
7 8
A = 98 23 12 11 23 6
12
>> A(8)=24;
>> A

2 Appending vector y to vector x
>> z= [x,y]
>> z= [x ; y]
z = 98 23 12 11 23 11 24 15 16 17
1 2 3 4 5 6 7 8 9 10
y = 11 24 15 16 17
1 2 3 4 5
x = 98 23 12 11 231 2 3 4 5
Z =
98 23 12 11 231 3 5 7 9
11 24 15 16 17
2 4 6 8 10

3 Adding elements to a matrix Adding new rows and/ or columns
A =
98 23 12 111 3 5 7
11 24 15 16
2 4 6 8
>>A(3,:)=4:4:16
A =
98 23 12 111 4 7 10
11 24 15 16
2 5 8 11
4 8 12 16
3 6 9 12
>>A(:,5)= 4:2:6
A =
98 23 12 111 3 5 7 9
11 24 15 16
2 4 6 8 10
4
6
Adding new row
Adding new column

Appending a new matrix to the existing one
>> C = [B A] >> B(5,5)= 333

Deleting elements of an existing arrays

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