# How to write summation in matlab with two variables?

24 ビュー (過去 30 日間)
Alicia 2021 年 4 月 21 日

I am having trouble transferring these formulas onto matlab. My code compiles, however, my variables are all 1x1 and 0. I'm not sure why it is not calculating these values using my data properly. Here is my code so far:
syms u(i) v(i)
ubar = (1/N)*symsum(u,i,1,N);
uprime2 = (1/N)*symsum(u-ubar,i,1,N);
vbar = (1/N)*symsum(v,i,1,N);
vprime2 = (1/N)*symsum(v-vbar,i,1,N);
uprimevprime = (1/N)*symsum((u-ubar)*(v-vbar),i,1,N);
##### 2 件のコメント表示 1 件の古いコメント非表示 1 件の古いコメント
Alicia 2021 年 4 月 22 日
Yes, u represents the 2D matrix of the u-component of the velocity on the vector grid with likely erroneous vectors replaced by NaN with units of m/s, and v represents the 2D matrix of the v-component of the velocity on the vector grid with likely erroneous vectors replaced by NaN with units of m/s

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### 採用された回答

Paul Hoffrichter 2021 年 4 月 21 日
I am new to sym, so I thought I would give this a try. Please check carefully, as I did not have time to do so. I hope you are doing this in Live Editor. Will be back in 16 hours to see if any problems.
N=4;
u = (sym('u%d',[1 N])).';
ubar = mean(u);
u_ubar = (u - ubar);
uprime2 = mean( u_ubar.^2);
v = (sym('v%d',[1 N])).';
vbar = mean(v)
v_vbar = (v - vbar)
vprime2 = mean(v_vbar.^2)
uprimevprime = mean(dot(u_ubar, v_vbar)) ##### 1 件のコメント表示 なし非表示 なし
Alicia 2021 年 4 月 22 日
That gave me much better results, I am not receiving any 0 values anymore. Thank you for your help

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