MATLAB中矩阵元素求和的方法有哪些? [英] What are the ways to sum matrix elements in MATLAB?

问题描述

给定矩阵:

A = [1 2 3; 4 5 6; 7 8 9];

1. 如何使用 for 循环来计算矩阵中元素的总和?
2. 使用函数 sum 编写一行 MATLAB 命令来求和A 中的矩阵元素.

1. How could you use a for loop to compute the sum of the elements in the matrix?
2. Write a one line MATLAB command using the function sum to sum the matrix elements in A.

我的回答:

1)

for j=1:3,
    for i=j:3,
        A(i,:) = A(i,:)+A(j+1,:)+A(j+2,:)
    end
end

2)

sum(A)

这些是正确的答案吗?我不知道如何使用 if、while 和 for.谁能给我解释一下?

Are these the correct answers? I didn't know how to use if, while and for. Can anyone explain it to me?

推荐答案

对于非常大的矩阵，使用 sum(sum(A)) 可以比 sum(A(:)) 更快:

For very large matrices using sum(sum(A)) can be faster than sum(A(:)):

>> A = rand(20000);
>> tic; B=sum(A(:)); toc; tic; C=sum(sum(A)); toc
Elapsed time is 0.407980 seconds.
Elapsed time is 0.322624 seconds.

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