How to solve this equation Numerically [VPASOLVE]

Hi there,

When i try to numerically solve my equation i got the following error :

Error using mupadengine/feval_internal (line 172)

More equations than variables is only supported for polynomial systems.

I simplified the equation to give you an example, and here is the equation example (the matlab code):

syms Idn
%%data
    Ism=200;
    Wb=1500;
    speedend=6000;
    Vsm=100;
    Ws=Wb:15:speedend;
    
    Eq2=Idn==sqrt(Idn)+(((2.4*10.^(-5))*(Idn).^2-0.013*(Idn+3.3)*10^(-3)))*Ws/Vsm %%The equation
    Idn=vpasolve(Eq2,Idn)

Can anyone help me to solve this kind of equation?

[Star Strider]

Probably not.

When I ran this:

syms Idn
%%data
Ism=200;
Wb=1500;
speedend=6000;
Vsm=100;
Ws=Wb:15:speedend;

Eq2=Idn==sqrt(Idn)+(((2.4*10.^(-5))*(Idn).^2-0.013*(Idn+3.3)*10^(-3)))*Ws/Vsm %%The equation
Idns=solve(Eq2,Idn)
Idn = simplify(vpa(Idns), 'Steps',150)

the result was:

Idns =
Empty sym: 0-by-1
 
Idn =
Empty sym: 0-by-1

.

Answer 1

[Alan Stevens]

You can solve it numerically using fzero.

Ism=200;
Wb=1500;
speedend=6000;
Ws=Wb:15:speedend;
Idn = zeros(size(Ws));
Idn0 = 1;
for i = 1:numel(Ws)
Idn(i) = fzero(@f,Idn0,[],Ws(i));
end

plot(Ws,Idn),grid
xlabel('Ws'),ylabel('Idn')

function  F = f(Idn,Ws)
    Vsm=100;
    F = sqrt(Idn)+(((2.4*10.^(-5))*(Idn).^2-0.013*(Idn+3.3)*10^(-3)))*Ws/Vsm-Idn; %%The equation
 end