How can I evaluate an objective function in matlab? Im trying to evaluate an objective funciton defined in matlab.

Hello there everyone,

I have the next problem

x = optimvar('x',4);

objec =(2*x(1))*(2*x(1))+(x(1)-x(4))*(x(1)-x(4))+(2*x(2)+x(3))*(2*x(2)+x(3))+(2+x(2))*(2+x(2))+x(3)*x(3)

prob = optimproblem('Objective',objec);

prob.Constraints.cons1 = x(1)+x(2) == 1;

prob.Constraints.cons2 = x(1) >= 0;

prob.Constraints.cons3 = x(2) >= 0;

problem = prob2struct(prob);

[x,fval1] = quadprog(problem)

which works fine and gives

x =

0.7143

0.2857

-0.2857

0.7143

fval1 =

3.4286

However, for other more general cases, I need to evaluate the objective function objec at (0,0,0,0) to check if there is a constant remaining (in this case, that constant is 4).

However, if I try to evaluate at y=[0 0 0 0]

val = evaluate(prob.Objective,y)

I get the error:

Error using optim.problemdef.OptimizationExpression/evaluate

Second argument must be a nonempty struct.

I wish to get the value val=4 but it is just not working.

Can someone give me some idea on this?

Thank you.

[Rachel Surridge]

Hello! The evaluate function expects a structure as its second argument. This structure should represent the point at which to evaluate. Try:

sol.x = [0 0 0 0]
val = evaluate(prob.Objective, sol)

[R. Can]

Thank you SOOO much. it does work.