An interactive introduction to MATLAB

1.4variables and arrays 11

Read MATLAB error messages!

??? Error using ==> mtimes

Inner matrix dimensions must agree.

This error message example usually indicates you tried to perform a matrix

operation when you intended an element-by-element operation. You should

check your code for a missing dot operator.

You can access individual elements, entire rows and columns, and subsets of

matrices using the notationmatrix_name(row,column). Listing 1.12 demon-

strates how to access elements in a matrix. Square brackets[ ]

are used when creating

vectors, arrays and

matrices, and round

brackets( )when

accessing elements in

them.

Listing 1.12: Accessing elements of matrices

1 >> w = [1 2 3 4; 5 6 7 8; 9 10 11 12]

2 w =

3 1 2 3 4

4 5 6 7 8

5 9 10 11 12

7 >> size(w)

8 ans =

9 3 4

11 >> w(1,1)
12 ans =
13 1

15 >> w(3,1)
16 ans =
17 9

19 >> w(3,:)
20 ans =
21 9 10 11 12

23 >> w(2,4) = 13
24 w =
25 1 2 3 4
26 5 6 7 13
27 9 10 11 12

29 >> v = w(1:2,2:3)
30 v =
31 2 3
32 6 7

34 >> z = w([2,3],[2,4])
35 z =
36 6 13
37 10 12