Finding x for y = f(x) in simulink

I have an equation which is uel = 3 + 3 * iel + 3 * log (3 * iel +1) a.k.a uel = f(iel) and I want to find iel ( uel is already known), so I have used fsolve to solve the problem in matlab and it works. Here is the code

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function iel = test(uel)

f = @(x) uel-(3 + 3 * x + 5 * log(3 * x + 1));

iel = fsolve(f,uel);

end

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But when i try to add this code into matlab function block in simulink, the model just don't run. I want my input to be uel and output to be iel. Can anyone please help me on this problem. Thank you so so much

[Max Heimann]

Can you provide the error message?

[Phan Van Long]

This is the error message sir @Max Heimann

Answer 1

[Paul]

According to the Symbolic Math Toolbox, the solution can be expressed as

%iel = wrightOmega(uel/3 - log(3) - 2/3) - 1/3

assuming that iel and uel are real. If they can be complex, the expression for iel is the same, but there are some other conditions that have to be satisfied.

Check

%doc wrightOmega

for more info.

Check a couple of test cases (note that I changed the 5 to a 3 in the function test() to match the equation in the question)

uel = 0.3

uel = 0.3000

iel = test(uel)

Equation solved.

fsolve completed because the vector of function values is near zero
as measured by the value of the function tolerance, and
the problem appears regular as measured by the gradient.

iel = -0.1723

iel = wrightOmega(uel/3 - log(3) - 2/3) - 1/3

iel = -0.1723

uel = 5.4

uel = 5.4000

iel = test(uel)

Equation solved.

fsolve completed because the vector of function values is near zero
as measured by the value of the function tolerance, and
the problem appears regular as measured by the gradient.

iel = 0.2465

iel = wrightOmega(uel/3 - log(3) - 2/3) - 1/3

iel = 0.2465

function iel = test(uel)
% f = @(x) uel-(3 + 3 * x + 5 * log(3 * x + 1)); % doesn't match equation in Question
f = @(x) uel-(3 + 3 * x + 3 * log(3 * x + 1));
iel = fsolve(f,uel);
end

Answer 2

[Dat Trương Lê Trí]

Hi, I am facing the same problem, did you have any posible solution for this case?