picos.reforms.reformulation

Backend for problem reformulation classes.

Outline

Classes

Reformulation

Base class for problem reformulations.

Classes

Reformulation

class picos.reforms.reformulation.Reformulation(theObject)[source]

Bases: abc.ABC

Base class for problem reformulations.

Abstract base class for a reformulation from one (possibly already reformulated) problem form to another.

__init__(theObject)[source]

Initialize Reformulation instances.

Parameters

theObject (Problem or Reformulation) – The input to work on; either an optimization problem or the (future) output of another reformulation.

abstract backward(solution)[source]

Translate back a solution from reformulated to original problem.

Transforms a single solution to output to a solution of input.

The method is allowed to modify the solution; it is not necessary to work on a copy. In particular, attach_to can be used if forward has created a deep copy of the problem.

execute()[source]

Reformulate the problem and obtain a solution from the result.

For this to work there needs to be a solver instance at the end of the reformulation pipeline, which would implement its own version of this method that actually solves the problem and produces the first solution.

abstract forward()[source]

Perform the initial problem reformulation.

Creates a modified copy or clone of the problem in input and stores it as output.

See copy and clone for the differences between a copy and a clone.

Implementations are supposed to do the necessary bookkeeping so that backward can transform a solution to the new problem back to a solution of the original problem.

abstract classmethod predict(footprint)[source]

Predict the reformulation’s effect on a problem footprint.

Given a problem footprint, returns another problem footprint that a problem with the former one would be reformulated to.

This is used to predict the effects of a reformulation when planning a solution strategy without the cost of actually transforming a problem.

reset()[source]

Reset the pipeline from this reformulation onward.

This is done whenever a reformulation does not implement update so that succeeding reformulations do not attempt to update a problem which was completely rewritten as this may be inefficient.

abstract classmethod supports(footprint)[source]

Whether the reformulation affects problems with the given footprint.

The reformulation must support every problem with such a footprint and the resulting problem should have a changed footprint.

abstract update()[source]

Update a previous problem reformulation.

Updates output and related bookkeeping information with respect to changes in input.

Raises

NotImplementedError – If performing an update is not feasible for the reformulation.

property input

The input problem.

output = None

The output problem.

successor = None

The next reformulation in the pipeline.

property verbosity

Verbosity level of the reformulation; same as for input problem.