PADEC - Coq Library

Library Padec.KDomSet.KDomSet_count_tree_topology

A Framework for Certified Self-Stabilization
PADEC Coq Library

Feb 2016

Global Imports

From Coq Require Import ZArith.
From Coq Require Import Lia.
From Coq Require Import SetoidList.
From Coq Require Import SetoidClass.
From Coq Require Import RelationPairs.

Local Imports

From Padec Require Import NatUtils.
From Padec Require Import OptionUtil.
From Padec Require Import SetoidUtil.
From Padec Require Import Count.
From Padec Require Import Algorithm.
From Padec Require Import RelModel.
From Padec Require Import Tree_topology.
From Padec Require Import KDomSet_algo_tree_topology.

Open Scope Z_scope.
Open Scope signature_scope.
Set Implicit Arguments.

How Many Elements in the k-Hop-Dominating Set?

Count the number of elements in the dominating set (dominating heads) built by the algorithm.

We prove bounds on it.

Section KDomSet_count.

Channel and Network definitions

  Context {Chans: Channels}
          {Net: Network}
          {DTN: Down_Tree_Network Net}
          {KDP: KDomSet_parameters}.
  Let k_pos := k_pos.

  Notation Tree := (DTN_topo (Net := Net)).
  Context {SPAN: is_spanning _ Tree}.

  Notation Algo := KDom_algo.
  Notation Env := (Env (Net := Net) (Algo := KDom_algo)).

  Existing Instance KDom_Stable.
  Existing Instance KDom_RO_assumption.

  Existing Instance alpha_compat.
  Existing Instance isParent_compat.
  Existing Instance isRoot_compat.

Assumptions on Inputs

  Variable (env: Env) (env_compat: Proper pequiv env)
           (hassume: Assume env)
           (final: terminal env).

Dominating Heads

Two kinds:

the regular one (with alpha equals k)
(maybe) the root

  Notation kDominator := (kDominator env).
  Definition DomHeads := { n : Node | kDominator n = true }.

  Notation eqDH := (equiv (A := DomHeads)).

Regular Dominating Heads are nodes such that alpha = k

  Definition RegDomHead p := alpha (env p) = k.

  Definition RegDomHeads := { n : Node | RegDomHead n }.

  Notation eqRDH := (equiv (A := RegDomHeads)).

  Global Instance RegDomHead_compat: Proper fequiv RegDomHead.

Regular Nodes are those below a tall node: They cannot be in the dominating set of the short root (if short)

  Inductive HasTallAncestor: Node -> Prop :=
  | HTA_self: forall n, alpha (env n) >= k -> HasTallAncestor n
  | HTA_parent:
      forall m n, isParent m n ->
                  HasTallAncestor m -> HasTallAncestor n.

  Definition RegNode := { n : Node | HasTallAncestor n }.

  Notation eqRN := (equiv (A := RegNode)).

  Global Instance HasTallAncestor_compat: Proper fequiv HasTallAncestor.

Relation between a node and its closest ancestor s.t. alpha=k

  Inductive RegHeadAncestor: Node -> Node -> Prop :=
  | RHA_self: forall n h, n == h -> alpha (env h) = k -> RegHeadAncestor n h
  | RHA_parent:
      forall m n h, isParent m n -> alpha (env n) <> k ->
                    RegHeadAncestor m h -> RegHeadAncestor n h.

  Global Instance RegHeadAncestor_compat:
    Proper fequiv RegHeadAncestor.

  Section with_cardinals.

    Variable (card_N: nat)
             (Hcard_N: Num_Card Same Node card_N).

    Variable (card_DH: nat)
             (Hcard_DH: Num_Card Same DomHeads card_DH).

    Variable (card_RDH: nat)
             (Hcard_RDH: Num_Card Same RegDomHeads card_RDH).

    Variable (card_RN: nat)
             (Hcard_RN: Num_Card Same RegNode card_RN).

Rcount is an existence witness for a the cardinality result

    Definition Rcount
               (cpl: ltN (Datatypes.S (Z.to_nat k)) * RegDomHeads)
               (rn: RegNode): Prop :=
      Z.to_nat (alpha (env (proj1_sig rn))) = proj1_sig (fst cpl) /\
      RegHeadAncestor (proj1_sig rn) (proj1_sig (snd cpl)).

count_ok every small index is present in every dominating set

Theorem simple_counting:
(card_RN >= (Datatypes.S (Z.to_nat k)) * card_RDH)%nat.

split_counting_cases if root is tall:

all dominating heads are regular
all nodes are regular (have a tall ancestor)

if root is short:

all dominating heads are regular except the root
at least one node is singular (namely the root)

    Lemma split_counting_cases:
      forall x: Node,
        (( card_DH =card_RDH /\ card_N = card_RN ) \/
         ( card_DH = Datatypes.S card_RDH /\ card_N >= Datatypes.S card_RN ))%nat.

    Theorem counting_theorem_assuming_cardinals_exist :
      forall x: Node,
        (card_N - 1 >= (Datatypes.S (Z.to_nat k)) * (card_DH - 1))%nat.

  End with_cardinals.

  Theorem counting_theorem_
          (card_N: nat)
          (Hcard_N: Num_Card Same Node card_N)
          (card_DH: nat)
          (Hcard_DH: Num_Card Same DomHeads card_DH) :
    forall x: Node,
      (card_N - 1 >= (Datatypes.S (Z.to_nat k)) * (card_DH - 1))%nat.

  Theorem counting_theorem_non_empty:
    forall x: Node,
    exists (card_N: nat) (card_DH: nat ),
      Num_Card Same Node card_N /\ Num_Card Same DomHeads card_DH /\
      (card_N - 1 >= (Datatypes.S (Z.to_nat k)) * (card_DH - 1))%nat.

  Theorem counting_theorem:
    exists (card_N: nat) (card_DH: nat ),
      Num_Card Same Node card_N /\ Num_Card Same DomHeads card_DH /\
      (card_N - 1 >= (Datatypes.S (Z.to_nat k)) * (card_DH - 1))%nat.

End KDomSet_count.

Close Scope Z_scope.
Close Scope signature_scope.
Unset Implicit Arguments.