Class TwoMaxEqualPeaks

java.lang.Object
org.cicirello.search.problems.TwoMaxEqualPeaks
All Implemented Interfaces:
IntegerCostOptimizationProblem<BitVector>, Problem<BitVector>

public final class TwoMaxEqualPeaks extends Object implements IntegerCostOptimizationProblem<BitVector>

This class implements a variation of the benchmarking problem known as TwoMax. The original TwoMax problem was defined as a problem with one global optima (the vector of all 1-bits) and a sub-optimal local optima (the vector of all 0-bits). For an implementation of the original TwoMax problem, see the TwoMax class. In the variation that we define here, we instead have two equally desirable global optima (one of these is the vector of all 1-bits, and the other is the vector of all 0-bits). We define it as follows. Maximize the function: f(x) = |20*CountOfOneBits(x) - 10*n|, where x is a vector of bits of length n. The two global optimal solutions have a maximal value of 10*n. This search landscape has two basins of attraction, which meet where the vector has an equal number of ones as zeros.

The value method implements the maximization version as described above. The algorithms of the Chips-n-Salsa library are defined for minimization, requiring a cost function. The cost method implements the equivalent as the following minimization problem: minimize cost(x) = 10*n - |20*CountOfOneBits(x) - 10*n|. The global optima are still all 1-bits or all 0-bits, each of which has a cost equal to 0.

  • Constructor Summary

    Constructors
    Constructor
    Description
    Constructs a TwoMaxEqualPeaks object for use in evaluating candidate solutions to the TwoMaxEqualPeaks problem, a variation of the TwoMax problem but with two globally optimal solutions, rather than one global optima and a local optima.
  • Method Summary

    Modifier and Type
    Method
    Description
    int
    cost(BitVector candidate)
    Computes the cost of a candidate solution to the problem instance.
    boolean
    isMinCost(int cost)
    Checks if a given cost value is equal to the minimum theoretical cost across all possible solutions to the problem instance, where lower cost implies better solution.
    int
    A lower bound on the minimum theoretical cost across all possible solutions to the problem instance, where lower cost implies better solution.
    int
    value(BitVector candidate)
    Computes the value of the candidate solution within the usual constraints and interpretation of the problem.

    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.problems.IntegerCostOptimizationProblem

    costAsDouble, getSolutionCostPair
  • Constructor Details

    • TwoMaxEqualPeaks

      public TwoMaxEqualPeaks()
      Constructs a TwoMaxEqualPeaks object for use in evaluating candidate solutions to the TwoMaxEqualPeaks problem, a variation of the TwoMax problem but with two globally optimal solutions, rather than one global optima and a local optima.
  • Method Details

    • cost

      public int cost(BitVector candidate)
      Description copied from interface: IntegerCostOptimizationProblem
      Computes the cost of a candidate solution to the problem instance. The lower the cost, the more optimal the candidate solution.
      Specified by:
      cost in interface IntegerCostOptimizationProblem<BitVector>
      Parameters:
      candidate - The candidate solution to evaluate.
      Returns:
      The cost of the candidate solution. Lower cost means better solution.
    • minCost

      public int minCost()
      Description copied from interface: IntegerCostOptimizationProblem
      A lower bound on the minimum theoretical cost across all possible solutions to the problem instance, where lower cost implies better solution. The default implementation returns Integer.MIN_VALUE.
      Specified by:
      minCost in interface IntegerCostOptimizationProblem<BitVector>
      Returns:
      A lower bound on the minimum theoretical cost of the problem instance.
    • value

      public int value(BitVector candidate)
      Description copied from interface: IntegerCostOptimizationProblem
      Computes the value of the candidate solution within the usual constraints and interpretation of the problem.
      Specified by:
      value in interface IntegerCostOptimizationProblem<BitVector>
      Parameters:
      candidate - The candidate solution to evaluate.
      Returns:
      The actual optimization value of the candidate solution.
    • isMinCost

      public boolean isMinCost(int cost)
      Description copied from interface: IntegerCostOptimizationProblem
      Checks if a given cost value is equal to the minimum theoretical cost across all possible solutions to the problem instance, where lower cost implies better solution.
      Specified by:
      isMinCost in interface IntegerCostOptimizationProblem<BitVector>
      Parameters:
      cost - The cost to check.
      Returns:
      true if cost is equal to the minimum theoretical cost,