Unable to assign a vpasolve result from a for loop

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

Answer 1

[Torsten]

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.

[Rihards]

Ah sorry, I had forgotten to add one of the pre-defined variables, which is Hb (they were all the way up in the original script). So I guess that leaves me to the fact that for D=0, k has no solution? How do I work around that?

[Torsten]

By setting

D = 0.5:0.5:110;

And still the question: Why do you solve for H0_t3 ?

H0_t3 = Hb*sqrt((1+G_var)*tanh(k_var*D(i)));

and all the variables on the right-hand side are known.

[Rihards]

.. must have been too focused on the wrong problem there. Thanks!