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Add Conventional Neural Evolution (CNE) optimizer.

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zoq committed Aug 27, 2017
1 parent 99ba553 commit 7af5fd18639740e2cf375333d17393dae39f045a
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* @file cne.hpp
* @author Marcus Edel
* @author Kartik Nighania
* Conventional Neural Evolution
* An optimizer that works like biological evolution which selects best
* candidates based on their fitness scores and creates new generation by
* mutation and crossover of population.
* mlpack is free software; you may redistribute it and/or modify it under the
* terms of the 3-clause BSD license. You should have received a copy of the
* 3-clause BSD license along with mlpack. If not, see
* for more information.
#include <mlpack/prereqs.hpp>
namespace mlpack {
namespace optimization {
* Conventional Neural Evolution (CNE) is a class of evolutionary algorithms
* focused on dealing with fixed topology. This class implements this algorithm
* as an optimization technique to converge a given function to minima.
* The algorithm works by creating a fixed number of candidates. The candidates
* are simply the network parameters that are untrained. Given the train and
* test set. Each candidate is tested upon the training set or 1 epoch and then
* a fitness score is assigned to it. Given the selection percentage of best
* candidates by the user, for a single generation that many percentage of
* candidates were selected for the next generation and the rest were removed
* The selected candidates for a particular generation then become the parent
* for the next generation and evolution takes place.
* The evolution process basically takes place in two types:
* - Crossover
* - Mutation
* Crossover takes two parents and generates two childs from them. Both the
* child have properties inherited by their parents. The parameters of the
* parents gets mixed using equal probability selection, creating two childs.
* This is just a mix of link weights or the parameters.
* In mutation parameters are updated by pertubating small noise.
* If \f$ \Lambda \f$ is the number of weights in the network.
* \f[ \sum_{n=1}^{\Lambda}\omega_n = \omega_n + \rho, \f]
* where \f$ \rho \f$ is the small pertubation value determined randomly between
* 0 and the mutation size given by the user as a constructor parameter. Also
* the mutation probability taken as a constructor parameter decides the amount
* of mutation addition into the network.
* Both the above mentioned process creates new candidates as well as changes
* the existing candidates to obtain better candidates in the next generated.
* The whole process then repeats for multiple generation until atleast one of
* the termination criteria is met:
* 1) The final value of the objective function (Not considered if not provided).
* 2) The maximum number of generation reached (optional but highly recommended).
* 3) Minimum change in best fitness values between two consecutive generations
* should be greater than a threshold value (Not considered if not provided).
* After which the final value and the parameters are returned by the optimize
* method.
* For CNE to work, a DecomposableFunctionType template parameter is required.
* This class must implement the following function:
* size_t NumFunctions();
* NumFunctions() should return the number of functions or data points in
* the dataset.
* double Evaluate(const arma::mat& coordinates, const size_t i);
* The parameter i refers to which individual function is being evaluated.
* The function will evaluate the objective function on the data point i in
* the dataset.
class CNE
* Constructor for the CNE optimizer.
* The default values provided over here are not necessarily suitable for a
* given function. Therefore it is highly recommended to adjust the
* parameters according to the problem.
* @param populationSize The number of candidates in the population.
* This should be atleast 4 in size.
* @param maxGenerations The maximum number of generations allowed for CNE.
* @param mutationProb Probability that a weight will get mutated.
* @param mutationSize The range of mutation noise to be added. This range
* is between 0 and mutationSize.
* @param selectPercent The percentage of candidates to select to become the
* the next generation.
* @param tolerance The final value of the objective function for termination.
* If set to negative value, tolerance is not considered.
* @param objectiveChange Minimum change in best fitness values between two
* consecutive generations should be greater than
* threshold. If set to negative value, objectiveChange is not
* considered.
CNE(const size_t populationSize = 500,
const size_t maxGenerations = 5000,
const double mutationProb = 0.1,
const double mutationSize = 0.02,
const double selectPercent = 0.2,
const double tolerance = 1e-5,
const double objectiveChange = 1e-5);
* Optimize the given function using CNE. The given
* starting point will be modified to store the finishing point of the
* algorithm, and the final objective value is returned.
* @tparam DecomposableFunctionType Type of the function to be optimized.
* @param function Function to optimize.
* @param iterate Starting point (will be modified).
* @return Objective value of the final point.
template<typename DecomposableFunctionType>
double Optimize(DecomposableFunctionType& function, arma::mat& iterate);
//! Get the population size.
size_t PopulationSize() const { return populationSize; }
//! Modify the population size.
size_t& PopulationSize() { return populationSize; }
//! Get maximum number of generations.
size_t MaxGenerations() const { return maxGenerations; }
//! Modify maximum number of generations.
size_t& MaxGenerations() { return maxGenerations; }
//! Get the mutation probability.
double MutationProbability() const { return mutationProb; }
//! Modify the mutation probability.
double& MutationProbability() { return mutationProb; }
//! Get the mutation size.
double MutationSize() const { return mutationSize; }
//! Modify the mutation size.
double& MutationSize() { return mutationSize; }
//! Get the selection percentage.
double SelectionPercentage() const { return selectPercent; }
//! Modify the selection percentage.
double& SelectionPercentage() { return selectPercent; }
//! Get the final objective value.
double Tolerance() const { return tolerance; }
//! Modify the final objective value.
double& Tolerance() { return tolerance; }
//! Get the change in fitness history between generations.
double ObjectiveChange() const { return objectiveChange; }
//! Modify the termination criteria of change in fitness value.
double& ObjectiveChange() { return objectiveChange; }
//! Reproduce candidates to create the next generation.
void Reproduce();
//! Modify weights with some noise for the evolution of next generation.
void Mutate();
* Crossover parents and create new childs.
* Two parents create two new childs.
* @param mom First parent from the elite population.
* @param dad Second parent from the elite population.
* @param dropout1 The place to delete the candidate of the present
* generation and place a child over there for the
* next generation.
* @param dropout2 The place to delete the candidate of the present
* generation and place a child over there for the
* next generation.
void Crossover(const size_t mom,
const size_t dad,
const size_t dropout1,
const size_t dropout2);
//! Population matrix. Each column is a candidate.
arma::cube population;
//! Vector of fintness values corresponding to each candidate.
arma::vec fitnessValues;
//! Index of sorted fitness values.
arma::uvec index;
//! The number of candidates in the population.
size_t populationSize;
//! Maximum number of generations before termination criteria is met.
size_t maxGenerations;
//! Number of candidates to become parent for the next generation.
size_t numElite;
//! Store the number of elements in a cube slice or a matrix column.
size_t elements;
//! The range of mutation noise to be added.
double mutationSize;
//! Probability that a weight will get mutated.
double mutationProb;
//! The percentage of best candidates to be selected for parents.
double selectPercent;
//! The final value of the objective function.
double tolerance;
//! Minimum change in best fitness values between two generations.
double objectiveChange;
} // namespace optimization
} // namespace mlpack
// Include implementation.
#include "cne_impl.hpp"
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