How to obtain the optimal parameter values for an objective function at certain values of objective function while using the fminunc function for optimization?

I am looking to optimize a non linear objective function with more than 15 variable using fminunc optimizer in Matlab Optimization toolbox. I want to obtain the values of variables/parameters as the objective function attains certain predefined values. How do I do it?

ht=matlabFunction(f,'vars',{z});
ll=rand(1,20);
options = optimoptions(@fminunc, 'OptimalityTolerance', 1e-1000,'MaxFunctionEvaluations',50000,'MaxIterations',5000,'FunctionTolerance',1e-100);
[xnew,fval]=fminunc(ht,ll,options);

Here, xnew denote the value of variables. I need values of xnew for a large number of predefined values of the objective function ht during the optimization process.

Answer 1

[Walter Roberson]

You would not use any minimizer for that. You would use fsolve() or vpasolve(), as in

F = @(z) ht(z) - predetermined_value)
parameters = fsolve(F, ll);