MATLAB diag Function Explained

The diag function is used to create a diagonal matrix. Here is the specific usage:

1. Create a diagonal matrix: The diag function takes a vector as input and returns a diagonal matrix with that vector as its diagonal elements.

A = [1 2 3];
B = diag(A);

% 结果是：
% B = 
% 1     0     0
% 0     2     0
% 0     0     3

1. Extract diagonal elements: The diag function can be used to extract the diagonal elements of a matrix.

C = [1 0 0; 0 2 0; 0 0 3];
D = diag(C);

% 结果是：
% D = 
% 1
% 2
% 3

1. Extract the k-th diagonal of a matrix: The elements of the k-th diagonal of a matrix can be extracted using the second parameter of the diag function.

E = [1 2 3; 4 5 6; 7 8 9];
F = diag(E, 1);

% 结果是：
% F = 
% 2
% 6

With these methods, the diag function can be used flexibly to operate on the elements of a diagonal matrix.