Assign variables from a solve solution

Hello!

I am having a slight problem where I am unable to assign the results of solve/vpa solve to a variable/variable array.

It has worked perfectly on an analogue problem in the previous parts of the same script, so I am unsure what I am missing here.

I am running the following for loop to find the solutions over the range of variable D2, and in this current setup the script runs well and gives me the solutions (correct), but as soon as I add "[Kr_x, alpha_x, k_x] = " in front of the vpasolve line, I'm getting the following error:

"Unable to find variables in equations"

Without the assignment to the three variables, I get the following answer:

ans =

struct with fields:

Kr_x: 0.99981170571100763658667832907699i

alpha_x: 97.041342847663022899757805866536

k_x: 0.029864918466521086498648092576702

So it seems like, it actually can find the variables?

syms k_x Kr_x alpha_x
c0=18.1499
alpha0=0.3491
g=9.81
omega=0.54

for i=1:length(D2)
    c_x=c0*tanh(k_x*D2(i));
    Snell_x=sin(alpha0)/c0==sin(alpha_x)/c_x;
    Defraction_x=Kr_x==sqrt(cos(alpha0)/cos(alpha_x));
    Linear_x = omega^2 == g*k_x*tanh(k_x*D2(i)); 
    vpasolve([Snell_x, Defraction_x, Linear_x],[Kr_x, alpha_x, k_x])
end

Answer 1

[Chunru]

syms k_x Kr_x alpha_x
c0=18.1499

c0 = 18.1499

alpha0=0.3491

alpha0 = 0.3491

g=9.81

g = 9.8100

omega=0.54

omega = 0.5400

D2 = [1 2];

for i=1:length(D2)
    c_x=c0*tanh(k_x*D2(i));
    Snell_x=sin(alpha0)/c0==sin(alpha_x)/c_x;
    Defraction_x=Kr_x==sqrt(cos(alpha0)/cos(alpha_x));
    Linear_x = omega^2 == g*k_x*tanh(k_x*D2(i)); 
    % one ouput struct
    sol(i) = vpasolve([Snell_x, Defraction_x, Linear_x],[Kr_x, alpha_x, k_x]);
end
sol(1)

ans = struct with fields:
       Kr_x: 0.97020769905214767846260313371713
    alpha_x: 100.5896791353776560831304307593
        k_x: 0.17326753619233916799563671436781

sol(2)

ans = struct with fields:
       Kr_x: 0.97103085879234422686236899857365i
    alpha_x: 97.306705145538144269628933596149
        k_x: 0.12313256334502620836110299915066

[Rihards]

I am unsure what I am looking at exactly. I noticed that I forgot to move the D2 value inside this example, but that is defined in the previous part. Sorry for that.

The output gives me the error when I try to run it like this:

[Kr_x, alpha_x, k_x] = vpasolve([Snell_x, Defraction_x, Linear_x],[Kr_x, alpha_x, k_x])

Ideally I would want to have a result stacked up in arrays of Kr_x(i) for example.

[Chunru]

vpasolve can only have one output argument, as the sol in the anser above. If your want to save the sol for each D2 element, you can use sol(i) instead.

[Rihards]

Alright, in that case how do I assign the three different variables to their own arrays?

Like Kr_x(i), alpha_x(i)?

[Chunru]

See the update above. All your results are stored in struct array now.