How to write summation in matlab with two variables?

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Alicia 2021-4-21

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https://ww2.mathworks.cn/matlabcentral/answers/808305-how-to-write-summation-in-matlab-with-two-variables

编辑： Alicia 2021-4-22

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);

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Paul Hoffrichter 2021-4-21

编辑：Paul Hoffrichter 2021-4-21

Could you tell me what the last equation represents? I was a little surprised about the subscript i being used for both u and v.

Alicia 2021-4-22

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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Answer 1

Paul Hoffrichter 2021-4-21

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/808305-how-to-write-summation-in-matlab-with-two-variables#answer_680640

在 MATLAB Online 中打开

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))