Unable to assign a vpasolve result from a for loop

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Rihards 2022-10-26

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评论： Rihards 2022-10-26

Hello there,

It's been a little while since I last used matlab extensively and this little error here has been driving me nuts for hours now.

I have a very simple script that runs a for loop to calculate multiple variables with an end goal of acquiring two arrays for a plot D(i) and H_sol(i), however, the last line with H_sol(i) is giving me an error:

Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

If I remove the i index, it will run with no problems, so I am a little confused here. Why would it not allow me to have two values of D and H_sol that correspond to the same i value/index?

syms k H0_t3
g=9.81;
omega=0.54
Hb=8
D=0:0.5:110;
for i=1:length(D)
    eq1=omega^2==g*k*tanh(k*D(i));
    k_var=vpasolve(eq1,k,0.01);
    G_var=(2*k_var*D(i))/(sinh(2*k_var*D(i)));
    eq2=H0_t3==Hb*sqrt((1+G_var)*tanh(k_var*D(i)));
    H_sol(i)=vpasolve(eq2,H0_t3)
end

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Answer 1

Torsten 2022-10-26

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https://ww2.mathworks.cn/matlabcentral/answers/1836443-unable-to-assign-a-vpasolve-result-from-a-for-loop#answer_1084433

编辑：Torsten 2022-10-26

For D = 0, there is no solution for k. And why do you solve for H0_t3 ? If Hb does not depend on H0_t3, the equation for H0_t3 is already explicitly solved for this variable.