Module org.cicirello.chips_n_salsa
Class WeightedLongestProcessingTime
java.lang.Object
org.cicirello.search.problems.scheduling.WeightedLongestProcessingTime
 All Implemented Interfaces:
Splittable<ConstructiveHeuristic<Permutation>>
,ConstructiveHeuristic<Permutation>
This is an implementation of the weighted longest process time heuristic. This heuristic is
usually defined as choose the job j with smallest value of: h(j) = w[j] / p[j], where w[j]
is the earliness weight of job j, and p[j] is its processing time. However, our
constructive heuristic implementation, as well as our stochastic sampling implementations that
rely on constructive heuristics assume that larger heuristic values are preferred. The stochastic
sampling algorithms also assume that the heuristic's valuations are positive. So we redefine it
as follows: h(j) = S  w[j] / p[j], where as before w[j] is the earliness weight of job j,
and p[j] is its processing time. S is computed as: S =
MIN_H
 min(w[j] / p[j]). The
MIN_H
is a small nonzero value. In this way, we shift all of the h(j) values by a
constant amount such that all h(j) values are positive.
Field Summary

Constructor Summary
ConstructorDescriptionConstructs a WeightedLongestProcessingTime heuristic. 
Method Summary
Modifier and TypeMethodDescriptionfinal int
Gets the required length of complete solutions to the problem instance for which this constructive heuristic is configured.final Partial<Permutation>
createPartial
(int n) Creates an empty Partial solution, which will be incrementally transformed into a complete solution of a specified length.final Problem<Permutation>
Gets a reference to the instance of the optimization problem that is the subject of this heuristic.double
h
(Partial<Permutation> p, int element, IncrementalEvaluation<Permutation> incEval) Heuristically evaluates the possible addition of an element to the end of a Partial.Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods inherited from interface org.cicirello.search.ss.ConstructiveHeuristic
createIncrementalEvaluation, split

Field Details

MIN_H
public static final double MIN_HThe minimum heuristic value. If the heuristic value as calculated is lower than MIN_H, then MIN_H is used as the heuristic value. The reason is related to the primary purpose of the constructive heuristics in the library: heuristic guidance for stochastic sampling algorithms, which assume positive heuristic values (e.g., an h of 0 would be problematic). See Also:


Constructor Details

WeightedLongestProcessingTime
Constructs a WeightedLongestProcessingTime heuristic. Parameters:
problem
 The instance of a scheduling problem that is the target of the heuristic.


Method Details

h
Description copied from interface:ConstructiveHeuristic
Heuristically evaluates the possible addition of an element to the end of a Partial. Higher evaluations imply that the element is a better choice for the next element to add. For example, if you evaluate two elements, x and y, with h, and h returns a higher value for y than for x, then this means that y is believed to be the better choice according to the heuristic. Implementations of this interface must ensure that h always returns a positive result. This is because stochastic sampling algorithms such as HBSS and VBSS assume that the constructive heuristic returns only positive values. Parameters:
p
 The current state of the Partialelement
 The element under consideration for adding to the PartialincEval
 An IncrementalEvaluation of p. This method assumes that incEval is of the same runtime type as the object returned byConstructiveHeuristic.createIncrementalEvaluation()
. Returns:
 The heuristic evaluation of the hypothetical addition of element to the end of p. The higher the evaluation, the more important the heuristic believes that element should be added next. The intention is to compare the value returned with the heuristic evaluations of other elements. Individual results in isolation are not necessarily meaningful.

getProblem
Description copied from interface:ConstructiveHeuristic
Gets a reference to the instance of the optimization problem that is the subject of this heuristic. Specified by:
getProblem
in interfaceConstructiveHeuristic<Permutation>
 Returns:
 the instance of the optimization problem that is the subject of this heuristic.

createPartial
Description copied from interface:ConstructiveHeuristic
Creates an empty Partial solution, which will be incrementally transformed into a complete solution of a specified length. Specified by:
createPartial
in interfaceConstructiveHeuristic<Permutation>
 Parameters:
n
 the desired length of the final complete solution. Returns:
 an empty Partial solution

completeLength
public final int completeLength()Description copied from interface:ConstructiveHeuristic
Gets the required length of complete solutions to the problem instance for which this constructive heuristic is configured. Specified by:
completeLength
in interfaceConstructiveHeuristic<Permutation>
 Returns:
 length of solutions to the problem instance for which this heuristic is configured
