how_to_use_particle_swarm_optimisation

In particle.swarm.optimisation: Optimisation with Particle Swarm Optimisation

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)
library(rgl)

Call the library

set.seed(42)
library(particle.swarm.optimisation)

To use the Particle or the swarm we need to define a fitness function and a range of value.

range_of_value <- list(c(1,300),c(1,300),c(1,300))
fitness_function <- function(values){
  return(values[[1]]+values[[2]]+values[[3]])
}

The Particle Class

This class is used to create a Particle for the Particle Swarm Optimisation.

method new() (initialize):

Used to create the Particle, take different parameters:

• values_ranges : A list of ranges for each value of the Particle, his size need to be the same as values.
• values : A numeric vector, each number represented the position of the Particle.
• fitness_function : The function used to find the fitness (or the score) of the particle. It needs to take a list as input and return a single value.
• acceleration_coefficient : A vector of two values, one for c1 (personal coefficient) and one for c2 (global coefficient).
• inertia : A numeric who represent the inertia of the Particle (the effect of the current velocity on the next velocity).

exemple <- Particle$new(values_ranges = range_of_value,
                           values = c(50,120,187),
                           fitness_function = fitness_function,
                           acceleration_coefficient = c(0.3,0.4),
                           inertia = 0.4)
print(exemple)

method get_fitness()

Used to calculate the fitness of the Particle (with the fitness function)

exemple$get_fitness() # 50+120+187
print(exemple) 

method update()

Used to change the position of the Particle based on his personal best and Swarm best, it also changes the personal best if needed. It takes one param:

• swarm_best : best values of the swarm

print(paste('best fitness before :',exemple$personal_best_fitness,sep = ' '))
exemple$update(swarm_best = c(200,300,300)) # the swarm best is just a random value here
print(exemple)
print(paste('best fitness after :',exemple$personal_best_fitness,sep = ' '))

method update_personal_best_fitness()

This method is used to change the personal best values and fitness with the current values and fitness of the Particles.

exemple$update_personal_best_fitness() # do nothing because the update method of the previous chunck also call this method.

method print()

This method print the current values of the particle and the fitness.

print(exemple)
# or :
exemple$print()

The ParticleSwarm Class

This class is used to create the swarm and launch the PSO. As a user you just need to init the ParticleSwarm object with the $new method and launch the PSO with the $run method.

method new()

Used to create the ParticleSwarm object, take different parameters:

• ranges_of_values : A list of ranges for each value for the particles.
• fitness_function : The function used to find the fitness (or the score) of the particle. It needs to take a list as input and return a single value.
• acceleration_coefficient_range : A list with two vectors with the min and max for c1 and c2.
• max_it : maximum number of itération
• inertia : A numeric who represent the inertia of the particle (the effect of the current velocity on the next velocity)
• pop_size : number of particle in the swarm.

swarm_exemple <- ParticleSwarm$new(pop_size = 10,
                                    ranges_of_values = range_of_value,
                                    fitness_function = fitness_function,
                                    max_it = 10,
                                    values_names = list('a','b','c'),
                                    acceleration_coefficient_range = list(c(0,1),c(0,1)),
                                    inertia = 0.4)

method generate_pop()

The generate pop is the method used to create the population of particles. The values of the particles are randomly selected in the range of values, the same goes for the acceleration coefficient. There is no need to call this method because the run does it for us. It takes one parameter:

• verbose : if the methods do the print or not

swarm_exemple$generate_pop(verbose = FALSE)
print(swarm_exemple)

method move_the_swarm()

This method is used to move the particle in the swarm. it takes one argument:

• verbose : If the method print or not the result in the console

The swarm's move are based on the following equation: V(t+1) = V(t) * i + c1 * r1 * (pb - x(t)) + c2 * r2 * (gb - x(t)) x(t+1) = x(t) + V(t+1)

Where:

• V is the velocity
• t is the number of the iteration
• i is the inertia
• c1 and c2 are the acceleration coefficient
• r1 and r2 are two random value between 0 and 1 who follow a uniform distribution
• pb is the personal best value of the particle
• gb is the best value of the swarm
• x is the current value of the particle

swarm_exemple$move_the_swarm(verbose = FALSE)
print(swarm_exemple)

method save_pop()

This method is used to save the current population in a csv file, the result is a data frame with the particle in row and the values in col, the last col is the fitness of the particle.

swarm_exemple$save_pop()

method plot_the_swarm_2D()

this method is used to plot the swarm if the problem used two values (if there is 3 values you can use plot3D).

swarm_exemple$plot_the_swarm_2D(nb_it=0,save_file=FALSE)

method plot_the_swarm_3D()

this method is used to plot the swarm if the problem used three values. it take one param:

• nb_it : the number of the iteration used to save the plot

swarm_exemple$plot_the_swarm_3D(nb_it=0,save_file=FALSE)

method run()

This is the main method of the call, it call all the other method to do the PSO (you just need to call this method) It takes two params:

• plot TRUE or FALSE, it is used to plot or not the result of each iteration
• verbose TRUE or FALSE, it is used to display or not the result in the console

swarm_exemple$run(verbose = FALSE,plot = FALSE,save_file = FALSE)
print(swarm_exemple)

particle.swarm.optimisation documentation built on May 21, 2021, 9:06 a.m.