A(x,y)
A的x行y列元素
A(x,:)
A的x行子矩阵
A(:,y)
A的y列子矩阵
[x,y] = find(A>20)
找A中大于20的元素，索引以矩阵形式行给m，列给n
例子
A = [1 2 3; 4 5 6; 7 8 9];
[m,n] = find (A > 5)
m =
3
3
2
3
n =
1
2
3
3
Last modification：December 18, 2022
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