Adding More Features for Extracting Values from Solutions

[kwesiRutledge]

When a user creates a Solution object, they currently have a very hard to parse object in-hand.

It has:

• Values, a map[uint64]float64 which maps the variables of the symbolic math system (usually not known to the user) to optimal values of the variables,
• Objective, a float64 which corresponds to the optimal objective, and
• Status, a problem.OptimizationStatus which describes the status of the optimization solver at termination.

We want to make it easier to use the Values field. Can we create utilities that make it easy to:

• FindValueOf(symbolic.Variable); Find the value of a symbolic.Variable instead of the value associated with an index
• FindValueOfExpr(symbolic.Expression); Find the value of a complicated symbolic expression using the solution's known variables.

[kwesiRutledge]

Addressed with #17 , but feel free to open this back up if we want more features for it!

[kwesiRutledge]

Reopening this to say that we really need the following method:

solution.FindValueOfExpression(s solution.Solution, expr symbolic.Expression) (float64, error)