Class: Dither::Cpp::Graph

Inherits:
Object
  • Object
show all
Defined in:
lib/dither/chinese_postman_problem.rb

Defined Under Namespace

Classes: Edge

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(n) ⇒ Graph

Returns a new instance of Graph.



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# File 'lib/dither/chinese_postman_problem.rb', line 13

def initialize(n)

  @n = n
  @degree = Array.new(n).fill(0)
  @defined = Array.new(n).fill { |_| Array.new(n).fill(false) }
  @label = Array.new(n).fill { |_| Array.new(n).fill { |_| [] } }
  @c = Array.new(n).fill { |_| Array.new(n).fill(0.0) }
  @f = Array.new(n).fill { |_| Array.new(n).fill(0) }
  @edges = Array.new(n).fill { |_| Array.new(n).fill(0) }
  @cheapest_edge = Array.new(n).fill { |_| Array.new(n).fill(0) }
  @path = Array.new(n).fill { |_| Array.new(n).fill(0) }
  @initialized = true
end

Instance Attribute Details

#c ⇒ Object

Returns the value of attribute c.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def c
  @c
end

#cheapest_edge ⇒ Object

Returns the value of attribute cheapest_edge.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def cheapest_edge
  @cheapest_edge
end

#defined ⇒ Object

Returns the value of attribute defined.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def defined
  @defined
end

#degree ⇒ Object

Returns the value of attribute degree.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def degree
  @degree
end

#edges ⇒ Object

Returns the value of attribute edges.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def edges
  @edges
end

#f ⇒ Object

Returns the value of attribute f.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def f
  @f
end

#initialized ⇒ Object

Returns the value of attribute initialized.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def initialized
  @initialized
end

#label ⇒ Object

Returns the value of attribute label.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def label
  @label
end

#n ⇒ Object

Returns the value of attribute n.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def n
  @n
end

#neg ⇒ Object

Returns the value of attribute neg.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def neg
  @neg
end

#origin ⇒ Object

Returns the value of attribute origin.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def origin
  @origin
end

#path ⇒ Object

Returns the value of attribute path.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def path
  @path
end

#pos ⇒ Object

Returns the value of attribute pos.



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# File 'lib/dither/chinese_postman_problem.rb', line 9

def pos
  @pos
end

Class Method Details

.create(raw_graph) ⇒ Object 



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# File 'lib/dither/chinese_postman_problem.rb', line 38

def self.create(raw_graph)
  vertices = [].to_set
  raw_graph[:edges].each do |edge|
    vertices << edge[:src_vertex]
    vertices << edge[:dst_vertex]
  end

  graph = Graph.new(vertices.length)

  raw_graph[:edges].each do |edge|
    graph.add_edge(edge[:name], edge[:src_vertex], edge[:dst_vertex], 1)
  end
  graph.origin = raw_graph[:origin]
  graph
end

Instance Method Details

#add_edge(lab, u, v, cost) ⇒ Object 



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# File 'lib/dither/chinese_postman_problem.rb', line 54

def add_edge(lab, u, v, cost)
  @label[u][v] = [] unless defined[u][v]
  @label[u][v] << lab
  if !defined[u][v] || c[u][v] > cost
    @c[u][v] = cost
    @cheapest_edge[u][v] = edges[u][v]
    @defined[u][v] = true
    @path[u][v] = v
  end
  @edges[u][v] += 1
  @degree[u] += 1
  @degree[v] -= 1
  self
end

#check_valid ⇒ Object 



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# File 'lib/dither/chinese_postman_problem.rb', line 69

def check_valid
  (0...n).each do |i|
    raise Dither::Error, 'negative cycle' if c[i][i] < 0
    (0...n).each do |j|
      raise Dither::Error, 'not strongly connected' unless defined[i][j]
    end
  end
end

#cpp ⇒ Object 



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# File 'lib/dither/chinese_postman_problem.rb', line 28

def cpp
  initialized?
  least_cost_paths
  check_valid
  find_feasible
  while improvments do
  end
  print(origin)
end

#find_feasible ⇒ Object 



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# File 'lib/dither/chinese_postman_problem.rb', line 96

def find_feasible
  nn, np = 0, 0
  (0...n).each do |i|
    if degree[i] < 0
      nn += 1
    elsif degree[i] > 0
      np += 1
    end
  end

  @neg = Array.new(nn)
  @pos = Array.new(np)
  nn, np = 0, 0
  (0...n).each do |i|
    if degree[i] < 0
      @neg[nn] = i
      nn += 1
    elsif degree[i] > 0
      @pos[np] = i
      np += 1
    end
  end

  (0...nn).each do |u|
    i = neg[u]
    (0...np).each do |v|
      j = pos[v]
      @f[i][j] = -degree[i] < degree[j] ? -degree[i] : degree[j]
      @degree[i] += f[i][j]
      @degree[j] -= f[i][j]
    end
  end
end

#improvments ⇒ Object 



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# File 'lib/dither/chinese_postman_problem.rb', line 130

def improvments
  r = Graph.new(n)
  (0...neg.length).each do |u|
    i = neg[u]
    (0...pos.length).each do |v|
      j = pos[v]
      if edges[i][j] > 0
        r.add_edge(nil, i, j, c[i][j])
      end
      if f[i][j] != 0
        r.add_edge(nil, j, i, -c[i][j])
      end
    end
  end

  r.least_cost_paths
  (0...n).each do |i|
    if r.c[i][i] < 0
      k = 0
      kunset = true
      u = i
      begin
        v = r.path[u][i]
        if r.c[u][v] < 0 && (kunset || k > f[v][u])
          k = f[v][u]
          kunset = false
        end
        u = v
      end while u != i
      u = i
      begin
        v = r.path[u][i]
        if r.c[u][v] < 0
          @f[v][u] -= k
        else
          @f[u][v] += k
        end
        u = v
      end while u != i
      return true
    end
  end
  false
end

#initialized? ⇒ Boolean

Returns:

  • (Boolean)

Raises:



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# File 'lib/dither/chinese_postman_problem.rb', line 209

def initialized?
  raise Dither::Error, 'graph not initialized' unless initialized
  raise Dither::Error, 'origin not set' unless origin
  @initialized = false
end

#least_cost_paths ⇒ Object 



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# File 'lib/dither/chinese_postman_problem.rb', line 78

def least_cost_paths
  (0...n).each do |k|
    (0...n).each do |i|
      if defined[i][k]
        (0...n).each do |j|
          if defined[k][j] && (!defined[i][j] || c[i][j] > c[i][k]+c[k][j])
            @defined[i][j] = true
            @path[i][j] = path[i][k]
            @c[i][j] = c[i][k] + c[k][j]
            # negative cycle
            return if i == j && c[i][j] < 0
          end
        end
      end
    end
  end
end

#print(start) ⇒ Object 



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# File 'lib/dither/chinese_postman_problem.rb', line 175

def print(start)
  result = []
  v = start
  loop do
    skip = false
    u = v
    (0...n).each do |i|
      if f[u][i] > 0
        v = i
        @f[u][v] -= 1
        while u != v
          p = path[u][v]
          result << Edge.new(label[u][p][cheapest_edge[u][p]], u, p)
          u = p
        end
        skip = true
      end
    end

    next if skip

    v = -1
    (0...n).each do |i|
      if edges[u][i] > 0
        v = i if v == -1 || i != path[u][start]
      end
    end
    return result if v == -1
    result << Edge.new(label[u][v][edges[u][v] - 1], u, v)
    @edges[u][v] -= 1
  end
  result
end