I get an error using fsolve but I don't understand why?

I have get an error

Too many output arguments.

Error in @(r)calculate_f(r,alphai,phi,phi0,n,m,fraci) (line 21)

func = @(r) calculate_f(r, alphai, phi, phi0, n, m, fraci);

Failure in initial objective function evaluation. FSOLVE cannot continue.

function f = calculate_f(r, alphai, phi, phi0, n, m, fraci)

f = zeros(m, 1);

f(1) = log(alphai(1) / r(1)) + log(1.0 - phi0 / phi) - log(1 - ((1.0 - phi) / (1.0 - phi0))^(1.0 / n));

for j = 2:m

f(j) = f(j-1) + log(alphai(j) / r(j)) + log(r(j-1) / alphai(j-1) - fraci(j-1));

end

end

func = @(r) calculate_f(r, alphai, phi, phi0, n, m, fraci);

r0 = r * ones(m, 1);

options = optimoptions('fsolve', 'Algorithm', 'trust-region-dogleg', 'SpecifyObjectiveGradient', true, 'CheckGradients', false, 'ScaleProblem', 'jacobian', 'FunctionTolerance', phitol);

ri = fsolve(func, r0, options);

Answer 1

[Steven Lord]

Look at the description of the fun input argument on the documentation page for the fsolve function. The relevant part of that documentation:

"f the Jacobian can also be computed and the 'SpecifyObjectiveGradient' option is true, set by

options = optimoptions('fsolve','SpecifyObjectiveGradient',true)

the function fun must return, in a second output argument, the Jacobian value J, a matrix, at x."

Your function does not return a second output argument. Either have it return that second output argument or don't set 'SpecifyObjectiveGradient' to true.

[Arvind]

Thank you