54 multiplier models

[IsitaRex]

Closes #54

Changes

On the multipliers module we created a new class called cooper.multipliers.MultiplierModel, which predicts the value of the Lagrange multipliers associated with the equality or inequality constraints of a cooper.problem.ConstrainedMinimizationProblem. Additionally, we created a new Lagrangian formulation --> cooper.formulation.LagrangianFormulation that works with the created MultiplierModel class.

Testing

We tested the class multipliers.MultiplierModel with the simplest model. A linear model with a single output. The new Lagrangian Formulation was also tested.

References

This idea comes from the paper by Narasimhan et al. and we took their repository as reference.