Class: MHL::Particle

Inherits:
GenericParticle show all
Defined in:
lib/mhl/particle.rb

Instance Attribute Summary

Attributes inherited from GenericParticle

#attractor

Instance Method Summary collapse

Methods inherited from GenericParticle

#evaluate

Constructor Details

#initialize(initial_position, initial_velocity) ⇒ Particle

Returns a new instance of Particle.



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# File 'lib/mhl/particle.rb', line 7

def initialize(initial_position, initial_velocity)
  super(initial_position)
  @velocity = initial_velocity
end

Instance Method Details

#move(chi, c1, c2, swarm_attractor) ⇒ Object

move particle and update attractor



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# File 'lib/mhl/particle.rb', line 13

def move(chi, c1, c2, swarm_attractor)
  raise 'Particle attractor is nil!' if @attractor.nil?

  # update particle velocity and position according to the Constrained PSO
  # variant of the Particle Swarm Optimization algorithm:
  #
  # V_{i,j}(t+1) = \chi [ V_{i,j}(t) + \\
  #                       C_1 * r_{i,j}(t) * (P_{i,j}(t) - X_{i,j}(t)) + \\
  #                       C_2 * R_{i,j}(t) * (G_j(t) - X_{i,j}(t)) ] \\
  # X_{i,j}(t+1) = X_{i,j}(t) + V_{i,j}(t+1)
  #
  # see equation 4.30 of [SUN11].

  # update velocity
  @velocity = @velocity.zip(@position, @attractor[:position], swarm_attractor[:position]).map do |v_j,x_j,p_j,g_j|
    # everything is damped by inertia weight chi
    chi *
      #previous velocity
      (v_j +
      # "memory" component (linear attraction towards the best position
      # that this particle encountered so far)
      c1 * SecureRandom.random_number * (p_j - x_j) +
      # "social" component (linear attraction towards the best position
      # that the entire swarm encountered so far)
      c2 * SecureRandom.random_number * (g_j - x_j))
  end

  # update position
  @position = @position.zip(@velocity).map do |x_j,v_j|
    x_j + v_j
  end
end

#remain_within(constraints) ⇒ Object

implement confinement à la SPSO 2011. for more information, see equations 3.14 and 3.15 of [CLERC12].



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# File 'lib/mhl/particle.rb', line 48

def remain_within(constraints)
  @position = @position.map.with_index do |x_j,j|
    d_max = constraints[:max][j]
    d_min = constraints[:min][j]
    if x_j > d_max
      # puts "resetting #{j}-th position component #{x_j} to #{d_max}"
      x_j = d_max
      # puts "resetting #{j}-th velocity component #{@velocity[j]} to #{-0.5 * @velocity[j]}"
      @velocity[j] = -0.5 * @velocity[j]
    elsif x_j < d_min
      # puts "resetting #{j}-th position component #{x_j} to #{d_min}"
      x_j = d_min
      # puts "resetting #{j}-th velocity component #{@velocity[j]} to #{-0.5 * @velocity[j]}"
      @velocity[j] = -0.5 * @velocity[j]
    end
    x_j
  end
end