How to expand a summation with different indexes

1 次查看（过去 30 天）
SooShiant
SooShiant 2015-10-2
评论： Thorsten 2015-10-6
How to expand a summation with different indexes like this?
Any help would be appreciated.
  4 个评论
显示 2更早的评论
Stephen23
Stephen23 2015-10-2
@SooShiant: Please stop posting the same question again and again.
SooShiant
SooShiant 2015-10-2
@Stephen Cobeldick
That was different. This is numerical but that one you deleted was symbolical. Don't you know the symbolical answer?

请先登录，再进行评论。

请先登录，再回答此问题。

回答（4 个）

Thorsten
Thorsten 2015-10-2
sum(diff(f(1:4)).*n(1:3).*arrayfun(@(x) sum(m(x:end)), 3:5))
  7 个评论
显示 5更早的评论
Muthu Annamalai
Muthu Annamalai 2015-10-2
@Thorsten : nice solution exploiting fact that each sum is independent of the other index, i and j, we may use dot products to compute the inner loop, and repeat it again for index i. I wonder if there is also a way to do it with mesgrid() and matrix products.
SooShiant
SooShiant 2015-10-2
@Muthu Annamalai: don't you know the symbolical code?

请先登录，再进行评论。

Sean de Wolski
Sean de Wolski 2015-10-2
编辑：Sean de Wolski 2015-10-2
sum(diff(f(1:4)).*n(1:3).*sum(m(3:5)))
  5 个评论
显示 3更早的评论
Thorsten
Thorsten 2015-10-2
编辑：Thorsten 2015-10-2
Sean, yes, i is 1:3, so the starting index of j is 3:5, so the sum runs for j = 3:5 for i = 1, j = 4:5 for i = 2, and j = 5 for i = 3, i.e., assumes values sum(m(3:5)), sum(m(4:5)) and sum(m(5)) for i=1,2,3. You forgot to sum over the different m(j), as far as I can see.

请先登录，再进行评论。

SooShiant
SooShiant 2015-10-2
As I said I want a code to expand summation (algebraic) not to get a numerical answer. How bad is it. There is no way. May I need to try Mathematica. Can any one help with Mathematica?
  3 个评论
显示 1更早的评论
SooShiant
SooShiant 2015-10-2
I've seen this page before but as I said I'm new to matlab and need an emergency help. May you write down this code for me pleeeeeease??????????

请先登录，再进行评论。

SooShiant
SooShiant 2015-10-2
I need Matlab answer me:
I wonder how you experts can't writes such a simple code. May it relates to Matlab capabilities and should use Mathematica. Can anyone help with Mathematica?

类别

在 Help Center 和 File Exchange 中查找有关 Matrix Indexing 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by