How to calculate a sum?

1 次查看（过去 30 天）

P 2011-5-14

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/7416-how-to-calculate-a-sum

I have a sum S (the greek symbol) from p=0 to M-1, g=(Is/VT)*exp(x/VT); and I want: ans=1/M * sum(g*exp(-j*(2*pi/M)*p)). x is a 21x1 vector and i need an answer 21x21.

Please help!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Walter Roberson 2011-5-14

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/7416-how-to-calculate-a-sum#answer_10197

在 MATLAB Online 中打开

g=(Is/VT)*exp(x/VT);
1/M * sum(g * exp(-j*(2*pi/M).*(0:M-1)))

However, if x is a vector, you need to clarify what shape it is (row or column) and need to clarify whether you want matrix multiplication for the "g*exp" part or what you want to do if x is a vector.

6 个评论
显示 4更早的评论隐藏 4更早的评论

Walter Roberson 2011-5-14

If your x is 21x1 then what I proposed will produce a 21x1 output, not a 1 x 21. For example, size(sum((1:21).' * (0:4),2)) yields 21 1

Are you expecting a 21x21 matrix of different values, or are you wanting to copy the 21x1 matrix out to 21x21 ? If you want to copy it out to 21x21 then

repmat(1/M * sum(g * exp(-j*(2*pi/M).*(0:M-1)),2),1,21)

if you want all the rows to be the same, or

repmat((1/M * sum(g * exp(-j*(2*pi/M).*(0:M-1)),2)).',21,1)

if you want all the columns to be the same

P 2011-5-14