4.9: The end, size, length, numel, min, and max functions

The end Keyword

The keyword end can be used as an index. It means the last valid index in that dimension.

Example \(\PageIndex{1}\)

Using the end keyword.

matrixA = [10, 20, 30; 40, 50, 60];

num_1 = matrixA(end,1)   % last row, first column
num_2 = matrixA(end,:)   % entire last row
num_3 = matrixA(end)   % last element in column-major order

Solution

num_1 = 40

num_2 = [40 50 60]

num_3 = 60

length, size, and numel

MATLAB has several useful functions for describing the size of an array.

Function	What it returns
length(A)	The larger of the number of rows or columns
size(A)	The number of rows and columns
numel(A)	The total number of elements in the array

Example \(\PageIndex{2}\)

Using the length, size, and numel keywords.

matrixA = [10, 20, 30; 40, 50, 60];

num_1 = length(matrixA)
num_2 = size(matrixA)
num_3 = numel(matrixA)

Solution

num_1 = 3

num_2 = [2   3]

num_3 = 6

Finding Maximum and Minimum Values

The max and min functions work a little differently with 2D arrays than they do with 1D arrays. When you call max(A), MATLAB returns the maximum value in each column.

To find the maximum value in the entire matrix, flatten the matrix first using A(:).

max(A(:))  %returns the maximum value in the entire matrix

[M, I] = max(A(:))  %returns two values: M is the maximum value, and I is the linear index of that value in the flattened matrix.

Example \(\PageIndex{3}\)

Finding maximum and minimum values.

A = [10, 20, 30; 40, 50, 60];

value_1 = max(A)     % maximum of each column

value_2 = max(A(:))  % maximum of the entire matrix

value_3 = min(A(:))  % minimum of the entire matrix

value_4 = [M, I] = max(A(:))

Solution

value_1 =

   40   50   60

value_2 = 60
value_3 = 10
value_4 = 60