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# Semirings for directed acyclic graphs (dags) (also directed hypergraphs),
# as described in:
# 'Dynamic Programming Algorithms in
# Semiring and Hypergraph Frameworks' (Liang Huang)
class Semiring
attr_accessor :add, :multiply, :one, :null, :convert
end
class BooleanSemiring < Semiring
def initialize
@add = Proc.new { |a,b| a||b }
@multiply = Proc.new { |a,b| a&&b }
@one = true
@null = false
@convert = Proc.new { |v| true && v!=0 }
end
end
class ViterbiSemiring < Semiring
def initialize
@add = Proc.new { |a,b| [a,b].max }
@multiply = Proc.new { |a,b| a*b }
@one = 1.0
@null = 0.0
@convert = Proc.new { |v| v }
end
end
class ViterbiLogSemiring < Semiring
def initialize
@add = Proc.new { |a,b| [a,b].max }
@multiply = Proc.new { |a,b| a+b }
@one = 0.0
@null = -1.0/0.0
@convert = Proc.new { |v| v }
end
end
class InsideSemiring < Semiring
def initialize
@add = Proc.new { |a,b| a+b }
@multiply = Proc.new { |a,b| a*b }
@one = 1.0
@null = 0.0
@convert = Proc.new { |v| v }
end
end
class RealSemiring < Semiring
def initialize
@add = Proc.new { |a,b| [a,b].min }
@multiply = Proc.new { |a,b| a+b }
@one = 0.0
@null = 1.0/0.0
@convert = Proc.new { |v| v }
end
end
# for longest/worst paths
class RealxSemiring < Semiring
def initialize
@add = Proc.new { |a,b| [a,b].max }
@multiply = Proc.new { |a,b| a+b }
@one = -1.0/0.0
@null = 0.0
@convert = Proc.new { |v| v }
end
end
class CountingSemiring < Semiring
def initialize
@add = Proc.new { |a,b| a+b }
@multiply = Proc.new { |a,b| a*b }
@one = 1.0
@null = 0.0
@convert = Proc.new { |v| if v!=0 then 1 else 0 end }
end
end
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