MATLAB Programming

1 Data Structures
Getting Information About a Matrix
This section explains how to get the following information about an existing
matrix:
• “Dimensions of the Matrix” on page 1-24
• “Data Types Used in the Matrix” on page 1-25
• “Data Structures Used in the Matrix” on page 1-26
Dimensions of the Matrix
These functions return information about the shape and size of a matrix.
Function
length
ndims
numel
size
Description
Return the length of the longest dimension. (The length of a
matrix or array with any zero dimension is zero.)
Return the number of dimensions.
Return the number of elements.
Return the length of each dimension.
The following examples show some simple ways to use these functions. Both
use the 3-by-5 matrix A shown here:
rand('state', 0); % Initialize random number generator
A = rand(5) * 10;
A(4:5, :) = []
A =
9.5013 7.6210 6.1543 4.0571 0.5789
2.3114 4.5647 7.9194 9.3547 3.5287
6.0684 0.1850 9.2181 9.1690 8.1317
Example Using numel
Using the numel function, find the average of all values in matrix A:
sum(A(:))/numel(A)
ans =
1-24