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feat(library): weak duality of max-flow min-cut theorem #18996

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@amilchew amilchew commented May 12, 2023

Formalise and validate the weak duality of the max-flow min-cut theorem, i.e. the value of every flow is less than or equal to the capacity of every cut.

The rest of the max-flow min-cut theorem proof is commented out because it contains sorry.


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@amilchew amilchew added the awaiting-review The author would like community review of the PR label May 12, 2023
@amilchew amilchew requested a review from a team as a code owner May 12, 2023 10:41
@amilchew amilchew changed the title Max flow min cut feat(library):weak duality of max-flow min-cut theorem May 12, 2023
@amilchew amilchew changed the title feat(library):weak duality of max-flow min-cut theorem feat(library): weak duality of max-flow min-cut theorem May 12, 2023
leanpkg.toml Outdated
@@ -5,3 +5,4 @@ lean_version = "leanprover-community/lean:3.50.3"
path = "src"

[dependencies]
mathlib = {git = "https://github.com/leanprover-community/mathlib", rev = "290a7ba01fbcab1b64757bdaa270d28f4dcede35"}
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This doesn't make any sense in mathlib itself!

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Removed.

Comment on lines 814 to 821
-- /-!
-- Here is our second big lemma, if the active flow is maximum,
-- then no augmenting path exists in the residual network.
-- -/

-- lemma no_augm_path {V : Type*} [inst' : fintype V]
-- (rsn : residual_network V) : (is_max_flow rsn.afn) -> no_augmenting_path rsn :=
-- begin
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If this is intended to be part of a later PR, you should just delete it from this one.

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Removed.

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@eric-wieser eric-wieser May 12, 2023

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This should either be:

  • Hosted on your own website / arxiv, and linked from references.bib
  • Put in the module docstring, or in various smaller docstrings throughout the file. Note that the doc website supports LaTeX in $$s

(is_edge : V → V → Prop)
(nonsymmetric : ∀ u v : V, ¬ ((is_edge u v) ∧ (is_edge v u)))

structure capacity (V : Type*) [inst : fintype V]
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To me this looks like it would work better as

Suggested change
structure capacity (V : Type*) [inst : fintype V]
structure capacity {V : Type*} [inst : fintype V] (g : digraph V)

Which says "a capacity on a particular graph". I assume you don't ever need to compare capacities between different graphs?

@kim-em kim-em added the too-late This PR was ready too late for inclusion in mathlib3 label Jul 16, 2023
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3 participants