# How to write summation in matlab with two variables?

11 vues (au cours des 30 derniers jours)
Alicia le 21 Avr 2021
Modifié(e) : Alicia le 22 Avr 2021
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 le 21 Avr 2021
Modifié(e) : Paul Hoffrichter le 21 Avr 2021
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 le 22 Avr 2021
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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### Réponse acceptée

Paul Hoffrichter le 21 Avr 2021
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 commentaireAfficher -1 commentaires plus anciensMasquer -1 commentaires plus anciens
Alicia le 22 Avr 2021
That gave me much better results, I am not receiving any 0 values anymore. Thank you for your help

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