Evaluate objective function without parsing

[jcavat]

Provide a function that evaluate the objective function who may have been returned by the run function.

Maybe something like:

let (solver_status, values, objective) = solver::run(&prob).unwrap();

[zappolowski]

I'm not sure whether the objective should be unconditionally evaluated. There are use cases where its actual value isn't important, but just the values of the variables is of interest.

Thus, I propose to make it two step:

let (status, values) = solver.run(&problem).unwrap();
let objective = problem.eval(&values);

eval is just the name I've used and I'm open for better suggestions. Another benefit of this approach is its backward compatibility.

Alternatively it might be a better to wrap the return value of solver.run into its own struct (e.g. named Solution), which then provides ways of retrieving status, values and objective.

[jcavat]

It's a good point. Returning a Solution structure seems a good ideal. Especially if we add new features such as eval. Maybe a Solution should refer to a Problem. With this, we could call eval without giving parameters.

[jcavat]

Create a new issue for that : #39