Matlab matrix index problem

matlab Matrix index problem

Always meet matlab Matrix index problem , You have to check the information every time to remember , Just sum up today , There are several cases ：
1. Matrix index to extract sub matrix

2. Find the index of matrix elements that meet the conditions
use find（） Function to find the index of non-zero elements , The grammar is as follows ：

k = find(X)
k = find(X,n)
k = find(X,n,direction)
[row,col] = find(___)
[row,col,v] = find(___)

k = find(X) Returns an array containing X Vector of linear index of each non-zero element in .

If X Vector , be find The return direction is the same as X The same vector .
If X For multidimensional arrays , be find Returns the column vector consisting of the linear index of the result .
If X Contains non-zero elements or is empty , be find Returns an empty array .

k = find(X,n) Return and X The non-zero element in the corresponding front n An index .
k = find(X,n,direction)（ among direction by ‘last’） Find and X The last of the nonzero elements in n An index .direction The default value is ‘first’, That is, find the first... Corresponding to non-zero elements n An index .
[row,col] = find(___) Use any of the input parameters in the previous syntax to return an array X Row and column subscripts for each non-zero element in .
[row,col,v] = find(___) Also returns contains X Vector of non-zero elements of v.
3. The index matrix can be used to determine the elements in the matrix

Example ： For one 1080*1920 In terms of the picture matrix , Give each pixel a color . The specific index is shown in the figure above . among k0 Index matrix （ Its size is the same as that of the image matrix ）, The elements stored inside are color matrix tmp（ The values stored inside can be understood as different colors ） The sequence number of the element in the . therefore , For pixels （1,1） Come on , Its color is tmp（k0）=x3.
Then there are other situations , And then add ！

If there is a problem , Welcome to correct !!