Alternating paths algorithm

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Algorithmic problem: The graph [math]\displaystyle{ G }[/math] is biparite.

Type of algorithm: loop

Auxillary data:

Abstract view

Invariant: Before and after each iteration, [math]\displaystyle{ M }[/math] is a matching.

Variant: [math]\displaystyle{ |M| }[/math] increases by [math]\displaystyle{ 1 }[/math].

Break condition: There is no more augmenting alternating path.

Induction basis

Abstract view: [math]\displaystyle{ M }[/math] is initialized to be some matching, for example, [math]\displaystyle{ M:=\empty }[/math].

Implementation: Obvious.

Proof: Nothing to show.

Induction step

Abstract view: If there is an augmenting alternating path, use it to increase [math]\displaystyle{ M }[/math]; otherwise, terminate the algorithm and return [math]\displaystyle{ M }[/math].

Implementation:

  1. Call the algorithm Find augmenting alternating path.
  2. If this call fails, terminate the algorithm and return [math]\displaystyle{ M }[/math].
  3. Otherwise, let [math]\displaystyle{ E' }[/math] denote the set of all edges on the path delivered by that call.
  4. Let [math]\displaystyle{ M }[/math] be the symmetric difference of [math]\displaystyle{ M }[/math] and [math]\displaystyle{ ??? }[/math]

Correctness:

Complexity

Statement:

Proof:

Further information