How do I add the sum of 1st 3 elements of a vector in a for loop?

Question

rezheen 2025-6-12

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2177752-how-do-i-add-the-sum-of-1st-3-elements-of-a-vector-in-a-for-loop

编辑： Stephen23 2025-6-12

I'd like for my for loop to end at n-1 as I have other code in the body. I just want to add a line in the for loop to add the sum of the 1st 3 elements underneath the left end points in the for loop and display it outside

t=0:5; a=[32 19.41 11.77 7.14 4.33 2.63];     
n=length(a); a1=a(1:3);
S=0; 
for k=1:n-1;
    S=S+sum(a(k));  % left end-points = upper estimate because a is decreasing
end
disp(S)

I'd like the code to do this with the desired output:

S = 32+ 51.41 + 63.18 = 146.59

2 个评论
显示无隐藏无

Walter Roberson 2025-6-12

在 MATLAB Online 中打开

S=S+sum(a(1:k));

rezheen 2025-6-12

在 MATLAB Online 中打开

In this case it's:

S=S+sum(a(1:k-2));

Thanks.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Stephen23 2025-6-12

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2177752-how-do-i-add-the-sum-of-1st-3-elements-of-a-vector-in-a-for-loop#answer_1566456

编辑：Stephen23 2025-6-12

在 MATLAB Online 中打开

a = [32,19.41,11.77,7.14,4.33,2.63];
m = 3;
s = sum(cumsum(a(1:m)))
s = 146.5900

or

s = a(1:m)*(m:-1:1).'
s = 146.5900

or

s = dot(a(1:m),m:-1:1)
s = 146.5900

or

s = sum(a(1:m).*(m:-1:1))
s = 146.5900

or

s = sum(a(1:m)*triu(ones(m)))
s = 146.5900

or

s = sum(repelem(a(1:m),m:-1:1))
s = 146.5900

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

rezheen 2025-6-12

That also works.

请先登录，再进行评论。

How do I add the sum of 1st 3 elements of a vector in a for loop?

2 个评论
显示无隐藏无

采纳的回答

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

更多回答（0 个）

另请参阅

类别

标签

产品

版本

Community Treasure Hunt

How do I add the sum of 1st 3 elements of a vector in a for loop?

2 个评论 显示 无隐藏 无

采纳的回答

1 个评论 显示 -1更早的评论隐藏 -1更早的评论

更多回答（0 个）

另请参阅

类别

标签

产品

版本

Community Treasure Hunt

2 个评论
显示无隐藏无

1 个评论
显示 -1更早的评论隐藏 -1更早的评论