向量的累积总和-语法 [英] Cumulative Sum of a Vector - Syntax

问题描述

我正在尝试解决以下Matlab语法不起作用的原因.

I am trying to resolve why the following Matlab syntax does not work.

1. 我有一个数组 A = [2 3 4 5 8 9 ...]
2. 例如，我希望创建一个索引累加 s(1)= 2; s(2)= 5，s(3)= 9; ...等等

1. I have an array A = [2 3 4 5 8 9...]
2. I wish to create an indexed cumulative, for example s(1) = 2; s(2)=5, s(3)=9; ... and so on

有人可以解释以下原因为何

Can someone please explain why the following does not work

x = 1:10
s(x) = sum(A(1:x))

逻辑是，如果使用x为s创建向量，为什么sum函数的行为不一样?上面的代码只返回所有x的第一个元素(2).

The logic is that if a vector is created for s using x, why would not the sum function behave the same way? The above returns just the first element (2) for all x.

推荐答案

要计算累加和，应使用cumsum:

For calculating the cumulative sum, you should be using cumsum:

>> A = [2 3 4 5 8 9]

A =

     2     3     4     5     8     9

>> cumsum(A)

ans =

     2     5     9    14    22    31

问题在于1:x是1，而sum减少了线性数组.要正确执行此操作，您需要一个2D数组，然后对行求和:

The issue is that 1:x is 1 and that sum reduces linear arrays. To do this properly, you need a 2d array and then sum the rows:

s(x)=sum(triu(repmat(A,[prod(size(A)) 1])'))

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