Merge pull request 'Add a perturbation step to the VNS engine' (#305) from vns-perturbations into main

Reviewed-on: #305

app/jobs/table_simulator_job.rb

@@ -12,8 +12,8 @@ class TableSimulatorJob < ApplicationJob
     ActsAsTenant.with_tenant(Wedding.find(wedding_id)) do
       engine = VNS::Engine.new
 
-      engine.add_perturbation(Tables::Swap)
-      engine.add_perturbation(Tables::Shift)
+      engine.add_optimization(Tables::Swap)
+      engine.add_optimization(Tables::Shift)
 
       initial_solution = Tables::Distribution.new(min_per_table: MIN_PER_TABLE, max_per_table: MAX_PER_TABLE)
       initial_solution.random_distribution(Guest.potential.shuffle)

app/services/tables/wheel_swap.rb

@@ -0,0 +1,33 @@
+# Copyright (C) 2024-2025 LibreWeddingPlanner contributors
+
+# frozen_string_literal: true
+
+module Tables
+  class WheelSwap
+    private attr_reader :initial_solution
+    def initialize(initial_solution)
+      @initial_solution = initial_solution
+    end
+
+    def call(size = 1)
+      Rails.logger.debug { "WheelSwap with size: #{size}" }
+      new_solution = @initial_solution.deep_dup
+
+      selected_guests = []
+
+      size.times do
+        selected_guests += new_solution.tables.map(&:pop)
+      end
+
+      selected_guests.shuffle!
+
+      tables = new_solution.tables.cycle
+
+      tables.next << selected_guests.pop while selected_guests.any?
+
+      new_solution.tables.each(&:reset)
+
+      new_solution
+    end
+  end
+end

app/services/vns/engine.rb

@@ -4,6 +4,7 @@
 
 module VNS
   class Engine
+    PERTURBATION_SIZES = [1, 1, 1, 2, 2, 3].freeze
     class << self
       def sequence(elements)
         elements = elements.to_a
@@ -15,6 +16,11 @@ module VNS
       @target_function = function
     end
 
+    def add_optimization(klass)
+      @optimizations ||= Set.new
+      @optimizations << klass
+    end
+
     def add_perturbation(klass)
       @perturbations ||= Set.new
       @perturbations << klass
@@ -24,32 +30,58 @@ module VNS
 
     def run
       raise 'No target function defined' unless @target_function
-      raise 'No perturbations defined' unless @perturbations
+      raise 'No optimizations defined' unless @optimizations
       raise 'No initial solution defined' unless @initial_solution
 
-      @best_solution = @initial_solution
-      @best_score = @target_function.call(@best_solution)
+      @perturbations ||= Set.new
 
-      self.class.sequence(@perturbations).each do |perturbation|
-        optimize(perturbation)
+      @current_solution = @initial_solution
+      @best_score = @target_function.call(@current_solution)
+
+      run_all_optimizations
+
+      best_solution = @current_solution
+
+      50.times do
+        @current_solution = Tables::WheelSwap.new(best_solution).call(PERTURBATION_SIZES.sample)
+        @best_score = @target_function.call(@current_solution)
+        Rails.logger.debug { "After perturbation: #{@best_score}" }
+
+        run_all_optimizations
+
+        next unless best_solution.discomfort > @current_solution.discomfort
+
+        best_solution = @current_solution
+        Rails.logger.debug do
+          "Found better solution after perturbation optimization: #{@current_solution.discomfort}"
+        end
       end
 
-      @best_solution
+      best_solution
     end
 
     private
 
-    def optimize(perturbation_klass)
+    def run_all_optimizations
+      self.class.sequence(@optimizations).each do |optimization|
+        optimize(optimization)
+        Rails.logger.debug { "Finished optimization phase: #{optimization}" }
+      end
+      Rails.logger.debug { 'Finished all optimization phases' }
+    end
+
+    def optimize(optimization_klass)
       loop do
         optimized = false
 
-        perturbation_klass.new(@best_solution).each do |alternative_solution|
+        optimization_klass.new(@current_solution).each do |alternative_solution|
           score = @target_function.call(alternative_solution)
           next if score >= @best_score
 
-          @best_solution = alternative_solution.deep_dup
+          @current_solution = alternative_solution.deep_dup
           @best_score = score
           optimized = true
+          Rails.logger.debug { "[#{optimization_klass}] Found better solution with score: #{score}" }
 
           break
         end

config/initializers/ruby_extensions.rb

@@ -10,4 +10,10 @@ class Set
   def to_table
     Tables::Table.new(self)
   end
+
+  def pop
+    element = self.to_a.sample
+    self.delete(element)
+    element
+  end
 end

lib/tasks/vns.rake

@@ -8,8 +8,8 @@ namespace :vns do
 
       engine = VNS::Engine.new
 
-      engine.add_perturbation(Tables::Swap)
-      engine.add_perturbation(Tables::Shift)
+      engine.add_optimization(Tables::Swap)
+      engine.add_optimization(Tables::Shift)
 
       hierarchy = AffinityGroupsHierarchy.new
       initial_solution = Tables::Distribution.new(min_per_table: 8, max_per_table: 10, hierarchy:)

spec/services/tables/wheel_swap_spec.rb

@@ -0,0 +1,28 @@
+# Copyright (C) 2024-2025 LibreWeddingPlanner contributors
+
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+module Tables
+  RSpec.describe WheelSwap do
+    context 'when the solution has three tables' do
+      let(:initial_solution) do
+        Distribution.new(min_per_table: 3, max_per_table: 3).tap do |distribution|
+          distribution.tables << Set[:a, :b, :c].to_table
+          distribution.tables << Set[:d, :e, :f].to_table
+          distribution.tables << Set[:g, :h, :i].to_table
+        end
+      end
+
+      it 'swaps a random guest from each table with a guest from another table', :aggregate_failures do
+        result = described_class.new(initial_solution).call
+
+        expect(result.tables.size).to eq(3)
+        expect(result.tables.map(&:size)).to all(eq(3))
+
+        expect(result.tables.map(&:to_a).flatten).to match_array((:a..:i).to_a)
+      end
+    end
+  end
+end