Failure in initial objective function evaluation. FSOLVE cannot continue.

Hello, i'm trying to solve a nonlinear system of equations and I saw on the web that the function I should be looking for was "fsolve" (I am a beginner MATLAB user). I created my personal function as the following:

    function y = eita(x, alpha)
y(1) = 1.543*10^-5 * x + 0.57
y(2) =(44.092 / 0.89605 - x) - alpha
end

Then I opened another path to call fsolve:

    fun = @eita
x0= [0,0]
sol = fsolve(fun,x0)

But something is wrong with my code and I get this command box report:

    Subscripted assignment dimension mismatch.

    Error in eita (line 2)
y(1) = 1.543*10^-5 * x + 0.57

    Error in fsolve (line 230)
            fuser = feval(funfcn{3},x,varargin{:});

    Error in ha (line 3)
sol = fsolve(fun,x0)

    Caused by:
    Failure in initial objective function evaluation. FSOLVE cannot continue.

Answer 1

[Star Strider]

You have to choose between coding them as:

function y = eita(x, alpha)
    y(1) = 1.543E-5 * x + 0.57;
    y(2) = (44.092 / 0.89605 - x) - alpha;
end

alpha = 3;
x0 = 1;
sol = fsolve(@(x)eita(x,alpha), x0)

to optimise ‘x’ with fixed ‘alpha’, or:

function y = eita(xv)
    x = xv(1);
    alpha = xv(2);
    y(1) = 1.543E-5 * x + 0.57;
    y(2) = (44.092 / 0.89605 - x) - alpha;
end

x0 = [1; 1];
sol = fsolve(@(x)eita(x), x0)

if you want to optimise both parameters.

[Matheus Rodrigues]

It worked, thanks mate

[Star Strider]

As always, my pleasure.