MATLAB: Failure in initial objective function evaluation. FSOLVE cannot continue.

errorfsolve

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.

Best Answer

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.
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