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import Mathlib
import OAI.Combinatorics.MatchingCount.Graphs.Cumulative
namespace OAI
namespace MatchingFPRAS.FiniteChoice
open Finset
lemma tapeIndex_value (k : ℕ) (bits : Fin k → Bool) :
(tapeIndex k bits).val = ∑ i, (if bits i then 1 else 0)*2^i.val := by
change (finFunctionFinEquiv (fun i => finTwoEquiv.symm (bits i))).val = _
rw [finFunctionFinEquiv_apply]
apply sum_congr rfl; intro i _
cases bits i <;> simp [finTwoEquiv]
lemma tapeLaw_eq {r : ℕ} (p : Fin r → ℚ) (hs : ∑ i, p i = 1) (k : ℕ) :
tapeLaw p hs k = outputLaw p hs (pow_pos (by norm_num : 0 < (2:ℕ)) k) := by
funext i
have hcard : (univ.filter (fun bits : Fin k → Bool => chooseBits p hs k bits=i)).card =
(univ.filter (fun J : Fin (2^k) => choose p hs (pow_pos (by norm_num : 0 < (2:ℕ)) k) J=i)).card := by
calc
_ = ∑ bits : Fin k → Bool, if chooseBits p hs k bits=i then (1:ℕ) else 0 := by simp
_ = ∑ J : Fin (2^k), if choose p hs (pow_pos (by norm_num : 0 < (2:ℕ)) k) J=i then (1:ℕ) else 0 :=
by
simp only [chooseBits]
convert (tapeIndex k).sum_comp
(fun J : Fin (2^k) => if choose p hs (pow_pos (by norm_num : 0 < (2:ℕ)) k) J=i then (1:ℕ) else 0) using 1
congr 3
_ = _ := by simp
simp only [tapeLaw,outputLaw,hcard,Nat.cast_pow,Nat.cast_ofNat]
end MatchingFPRAS.FiniteChoice
namespace MatchingFPRAS.BoundedSimulation
open Finset
variable {Ω : Type*} [Fintype Ω] [DecidableEq Ω]
def runBits {r : ℕ} (z : Ω) (p : ℕ → Ω → Fin r → ℚ)
(hs : ∀ n s, ∑ i, p n s i = 1) (next : ℕ → Ω → Fin r → Ω) (k : ℕ) :
(n : ℕ) → (Fin n → Fin k → Bool) → Ω
| 0, _ => z
| n+1, bits =>
let s := runBits z p hs next k n (Fin.init bits)
next n s (MatchingFPRAS.FiniteChoice.chooseBits (p n s) (hs n s) k (bits (Fin.last n)))
def pointMass (z : Ω) (s : Ω) : ℚ := if z=s then 1 else 0
def uniformLaw {A : Type*} [Fintype A] (f : A → Ω) (s : Ω) : ℚ :=
(∑ a, if f a=s then (1:ℚ) else 0)/(Fintype.card A:ℚ)
omit [Fintype Ω] in
lemma uniformLaw_equiv [Fintype Ω] {A B : Type*} [Fintype A] [Fintype B] (e : A ≃ B)
(f : B → Ω) (s : Ω) : uniformLaw (f ∘ e) s=uniformLaw f s := by
unfold uniformLaw
rw [Fintype.card_congr e]
congr 1
exact e.sum_comp (fun b => if f b=s then (1:ℚ) else 0)
lemma fiber_sum {A : Type*} [Fintype A] (f : A → Ω) (g : Ω → ℚ) :
(∑ s, (∑ a, if f a=s then (1:ℚ) else 0)*g s) = ∑ a, g (f a) := by
simp_rw [sum_mul,ite_mul,one_mul,zero_mul]
rw [sum_comm]
simp only [sum_ite_eq,mem_univ,ite_true]
lemma uniformLaw_map {A Ψ : Type*} [Fintype A] [Fintype Ψ] [DecidableEq Ψ]
(f : A → Ω) (g : Ω → Ψ) (t : Ψ) :
uniformLaw (g ∘ f) t = ∑ s, uniformLaw f s*(if g s=t then 1 else 0) := by
unfold uniformLaw
simp only [Function.comp_apply,div_mul_eq_mul_div,← sum_div]
rw [fiber_sum]
lemma uniformLaw_prod {A B : Type*} [Fintype A] [Fintype B]
(f : A → Ω) (g : Ω → B → Ω) (t : Ω) :
uniformLaw (fun ab : A×B => g (f ab.1) ab.2) t =
∑ s, uniformLaw f s*uniformLaw (g s) t := by
unfold uniformLaw
simp only [Fintype.card_prod,Nat.cast_mul,div_mul_div_comm,← sum_div,Fintype.sum_prod_type]
rw [fiber_sum]
lemma uniformLaw_chooseBits {r : ℕ} (p : Fin r → ℚ) (hs : ∑ i, p i=1) (k : ℕ) (i : Fin r) :
uniformLaw (MatchingFPRAS.FiniteChoice.chooseBits p hs k) i =
MatchingFPRAS.FiniteChoice.outputLaw p hs (pow_pos (by norm_num : 0 < (2:ℕ)) k) i := by
rw [← MatchingFPRAS.FiniteChoice.tapeLaw_eq]
simp [uniformLaw,MatchingFPRAS.FiniteChoice.tapeLaw]
lemma uniformLaw_choice_step {r : ℕ} (p : Fin r → ℚ) (hs : ∑ i, p i=1) (k : ℕ)
(next : Fin r → Ω) (t : Ω) :
uniformLaw (fun bits => next (MatchingFPRAS.FiniteChoice.chooseBits p hs k bits)) t =
∑ i, if next i=t then MatchingFPRAS.FiniteChoice.outputLaw p hs
(pow_pos (by norm_num : 0 < (2:ℕ)) k) i else 0 := by
have h := uniformLaw_map (MatchingFPRAS.FiniteChoice.chooseBits p hs k) next t
simp only [uniformLaw_chooseBits,mul_ite,mul_one,mul_zero] at h
convert h using 1
congr 3
lemma runBits_law_succ {r : ℕ} (z : Ω) (p : ℕ → Ω → Fin r → ℚ)
(hs : ∀ n s, ∑ i, p n s i=1) (next : ℕ → Ω → Fin r → Ω) (k n : ℕ) (t : Ω) :
uniformLaw (runBits z p hs next k (n+1)) t =
categoricalStep (uniformLaw (runBits z p hs next k n))
(fun s => MatchingFPRAS.FiniteChoice.outputLaw (p n s) (hs n s)
(pow_pos (by norm_num : 0 < (2:ℕ)) k)) (next n) t := by
let e : ((Fin n → Fin k → Bool) × (Fin k → Bool)) ≃ (Fin (n+1) → Fin k → Bool) :=
(Equiv.prodComm _ _).trans (Fin.snocEquiv (fun _ => Fin k → Bool))
have hh := uniformLaw_equiv e (runBits z p hs next k (n+1)) t
have hc : (runBits z p hs next k (n+1)) ∘ e =
(fun ab : ((Fin n → Fin k → Bool) × (Fin k → Bool)) =>
next n (runBits z p hs next k n ab.1)
(MatchingFPRAS.FiniteChoice.chooseBits (p n (runBits z p hs next k n ab.1))
(hs n (runBits z p hs next k n ab.1)) k ab.2)) := by
funext ab
rcases ab with ⟨pref, last⟩
change next n (runBits z p hs next k n (Fin.init (Fin.snoc (α := fun _ : Fin (n+1) => Fin k → Bool) pref last)))
(MatchingFPRAS.FiniteChoice.chooseBits
(p n (runBits z p hs next k n (Fin.init (Fin.snoc (α := fun _ : Fin (n+1) => Fin k → Bool) pref last))))
(hs n (runBits z p hs next k n (Fin.init (Fin.snoc (α := fun _ : Fin (n+1) => Fin k → Bool) pref last)))) k
((Fin.snoc (α := fun _ : Fin (n+1) => Fin k → Bool) pref last) (Fin.last n))) = _
simp only [Fin.init_snoc,Fin.snoc_last]
rw [hc] at hh
rw [← hh,uniformLaw_prod (runBits z p hs next k n)
(fun s bits => next n s (MatchingFPRAS.FiniteChoice.chooseBits (p n s) (hs n s) k bits)) t]
simp only [uniformLaw_choice_step,categoricalStep]
lemma runBits_law {r : ℕ} (z : Ω) (p : ℕ → Ω → Fin r → ℚ)
(hs : ∀ n s, ∑ i, p n s i=1) (next : ℕ → Ω → Fin r → Ω) (k n : ℕ) :
uniformLaw (runBits z p hs next k n) = bitRun (pointMass z) p hs next k n := by
induction n with
| zero => funext s; by_cases h : z=s <;> simp [runBits,bitRun,uniformLaw,pointMass,h]
| succ n ih => funext s; rw [runBits_law_succ,ih]; rfl
omit [Fintype Ω] in
lemma pointMass_nonneg [Fintype Ω] (z : Ω) (s : Ω) : 0 ≤ pointMass z s := by
unfold pointMass; split_ifs <;> norm_num
lemma pointMass_sum (z : Ω) : ∑ s, pointMass z s=1 := by simp [pointMass]
lemma fixed_tape_card (n k : ℕ) : Fintype.card (Fin n → Fin k → Bool)=2^(n*k) := by
simp only [Fintype.card_fun,Fintype.card_bool,Fintype.card_fin,← pow_mul,Nat.mul_comm k n]
theorem fixed_tape_simulation {r : ℕ} (z : Ω) (p : ℕ → Ω → Fin r → ℚ)
(hp : ∀ n s i, 0 ≤ p n s i) (hs : ∀ n s, ∑ i, p n s i=1)
(next : ℕ → Ω → Fin r → Ω) (k n : ℕ) :
(∑ s, |uniformLaw (runBits z p hs next k n) s-idealRun (pointMass z) p next n s|)/2 ≤
2*n*r/(2:ℚ)^k := by
rw [runBits_law]
exact finite_bit_simulation (pointMass z) (pointMass_nonneg z) (pointMass_sum z) p hp hs next k n
end MatchingFPRAS.BoundedSimulation
namespace MatchingFPRAS.Counting
open Finset
abbrev alpha : ℚ := 1/100000
lemma others_nonempty {n : ℕ} (hn : 2 ≤ n) (i : Fin n) : (univ.erase i).Nonempty := by
let j : Fin n := ⟨if i.val=0 then 1 else 0, by split_ifs <;> omega⟩
refine ⟨j,mem_erase.mpr ⟨?_,mem_univ _⟩⟩
apply Fin.ne_of_val_ne
dsimp [j]; split_ifs <;> omega
def rowMaximum {n : ℕ} (hn : 2 ≤ n) (G : Fin n → Fin n → ℚ) (v : Fin n → ℚ) (i : Fin n) : ℚ :=
(univ.erase i).sup' (others_nonempty hn i) (fun j => G i j / v j)
def scaleUpdate {n : ℕ} (hn : 2 ≤ n) (G : Fin n → Fin n → ℚ) (v : Fin n → ℚ) (i : Fin n) : Fin n → ℚ :=
Function.update v i (rowMaximum hn G v i)
def scalingTrace {n : ℕ} (hn : 2 ≤ n) (G : Fin n → Fin n → ℚ) : ℕ → Fin n → ℚ
| 0 => fun _ => 2
| k+1 => if hk : k<n then scaleUpdate hn G (scalingTrace hn G k) ⟨k,hk⟩ else scalingTrace hn G k
open Finset
variable {n : ℕ}
structure ScaleInvariant (G : Fin n → Fin n → ℚ) (v : Fin n → ℚ) : Prop where
lower : ∀ i, alpha/2 ≤ v i
upper : ∀ i, v i ≤ 2
feasible : ∀ i j, i≠j → G i j ≤ v i*v j
lemma ScaleInvariant.pos {G : Fin n → Fin n → ℚ} {v : Fin n → ℚ}
(hv : ScaleInvariant G v) (i) : 0 < v i := lt_of_lt_of_le (by norm_num [alpha]) (hv.lower i)
lemma rowMaximum_le (hn : 2 ≤ n) (G : Fin n → Fin n → ℚ) (v : Fin n → ℚ)
(hv : ScaleInvariant G v) (i) : rowMaximum hn G v i ≤ v i := by
apply Finset.sup'_le
intro j hj
exact (div_le_iff₀ (hv.pos j)).mpr (hv.feasible i j (mem_erase.mp hj).1.symm)
lemma ratio_le_rowMaximum (hn : 2 ≤ n) (G : Fin n → Fin n → ℚ) (v : Fin n → ℚ)
(i j) (hji : j≠i) : G i j/v j ≤ rowMaximum hn G v i :=
Finset.le_sup' (fun j => G i j/v j) (mem_erase.mpr ⟨hji,mem_univ _⟩)
lemma rowMaximum_lower (hn : 2 ≤ n) (G : Fin n → Fin n → ℚ) (v : Fin n → ℚ)
(hG : ∀ i j, i≠j → alpha ≤ G i j) (hv : ScaleInvariant G v) (i) :
alpha/2 ≤ rowMaximum hn G v i := by
obtain ⟨j,hj⟩ := others_nonempty hn i
have hji := (mem_erase.mp hj).1
apply le_trans _ (ratio_le_rowMaximum hn G v i j hji)
apply (le_div_iff₀ (hv.pos j)).mpr
have hGi := hG i j hji.symm
have hvi := hv.upper j
norm_num [alpha] at *
linarith
lemma scaleUpdate_le (hn : 2 ≤ n) (G : Fin n → Fin n → ℚ) (v : Fin n → ℚ)
(hv : ScaleInvariant G v) (i j) : scaleUpdate hn G v i j ≤ v j := by
by_cases hji : j=i
· subst j; simpa [scaleUpdate] using rowMaximum_le hn G v hv i
· simp [scaleUpdate,Function.update_of_ne hji]
lemma scaleUpdate_invariant (hn : 2 ≤ n) (G : Fin n → Fin n → ℚ) (v : Fin n → ℚ)
(hsym : ∀ i j, G i j=G j i) (hG : ∀ i j, i≠j → alpha ≤ G i j)
(hv : ScaleInvariant G v) (i) : ScaleInvariant G (scaleUpdate hn G v i) := by
constructor
· intro j
by_cases hji : j=i
· subst j; simpa [scaleUpdate] using rowMaximum_lower hn G v hG hv i
· simpa [scaleUpdate,Function.update_of_ne hji] using hv.lower j
· intro j; exact (scaleUpdate_le hn G v hv i j).trans (hv.upper j)
· intro a b hab
by_cases hai : a=i
· subst a
have hb := (div_le_iff₀ (hv.pos b)).mp (ratio_le_rowMaximum hn G v i b hab.symm)
simpa [scaleUpdate,Function.update_of_ne hab.symm] using hb
· by_cases hbi : b=i
· subst b
have ha := (div_le_iff₀ (hv.pos a)).mp (ratio_le_rowMaximum hn G v i a hai)
simpa [scaleUpdate,Function.update_of_ne hai,hsym i a,mul_comm] using ha
· simpa [scaleUpdate,Function.update_of_ne hai,Function.update_of_ne hbi] using hv.feasible a b hab
lemma scaleUpdate_tight (hn : 2 ≤ n) (G : Fin n → Fin n → ℚ) (v : Fin n → ℚ)
(hv : ScaleInvariant G v) (i) :
∃ j, j≠i ∧ scaleUpdate hn G v i i*scaleUpdate hn G v i j=G i j := by
obtain ⟨j,hj,heq⟩ := Finset.exists_mem_eq_sup' (others_nonempty hn i) (fun j => G i j/v j)
have hji := (mem_erase.mp hj).1
refine ⟨j,hji,?_⟩
change rowMaximum hn G v i = G i j/v j at heq
simp only [scaleUpdate,Function.update_self,Function.update_of_ne hji]
rw [heq]
exact div_mul_cancel₀ _ (hv.pos j).ne'
lemma tight_persists (G : Fin n → Fin n → ℚ) (v v' : Fin n → ℚ)
(hv : ScaleInvariant G v) (hv' : ScaleInvariant G v') (hdown : ∀ i, v' i ≤ v i)
(i j) (hji : j≠i) (hij : v i*v j=G i j) : v' i*v' j=G i j := by
apply le_antisymm
· calc
_ ≤ v i*v j := mul_le_mul (hdown i) (hdown j) (hv'.pos j).le (hv.pos i).le
_ = _ := hij
· exact hv'.feasible i j hji.symm
lemma scalingTrace_invariant (hn : 2 ≤ n) (G : Fin n → Fin n → ℚ)
(hsym : ∀ i j, G i j=G j i) (hG : ∀ i j, i≠j → alpha ≤ G i j ∧ G i j ≤ 3)
(k : ℕ) : ScaleInvariant G (scalingTrace hn G k) ∧
∀ i, i.val<k → ∃ j, j≠i ∧ scalingTrace hn G k i*scalingTrace hn G k j=G i j := by
induction k with
| zero =>
constructor
· constructor
· intro i; norm_num [scalingTrace,alpha]
· intro i; simp [scalingTrace]
· intro i j h; have := (hG i j h).2; simp only [scalingTrace]; linarith
· intro i hi; omega
| succ k ih =>
by_cases hk : k<n
· let i : Fin n := ⟨k,hk⟩
have hinv := scaleUpdate_invariant hn G (scalingTrace hn G k) hsym (fun i j h => (hG i j h).1) ih.1 i
have htrace : scalingTrace hn G (k+1)=scaleUpdate hn G (scalingTrace hn G k) i := by
simp [scalingTrace,hk,i]
rw [htrace]
refine ⟨hinv,?_⟩
intro a ha
by_cases hak : a.val<k
· obtain ⟨j,hj,he⟩ := ih.2 a hak
refine ⟨j,hj,?_⟩
exact tight_persists G _ _ ih.1 hinv (scaleUpdate_le hn G _ ih.1 i) a j hj he
· have hai : a=i := Fin.ext (by dsimp [i]; omega)
subst a
exact scaleUpdate_tight hn G _ ih.1 i
· have htrace : scalingTrace hn G (k+1)=scalingTrace hn G k := by simp [scalingTrace,hk]
rw [htrace]
refine ⟨ih.1,?_⟩
intro i _
exact ih.2 i (by have := i.isLt; omega)
open Finset
theorem one_pass_scaling {n : ℕ} (hn : 2 ≤ n) (G : Fin n → Fin n → ℚ)
(hsym : ∀ i j, G i j=G j i) (hG : ∀ i j, i≠j → alpha ≤ G i j ∧ G i j ≤ 3) :
(∀ k i, scalingTrace hn G (k+1) i ≤ scalingTrace hn G k i) ∧
(∀ i, alpha/2 ≤ scalingTrace hn G n i ∧ scalingTrace hn G n i ≤ 2) ∧
(∀ i j, i≠j → G i j ≤ scalingTrace hn G n i * scalingTrace hn G n j) ∧
(∀ i, ∃ j, j≠i ∧ scalingTrace hn G n i * scalingTrace hn G n j=G i j) := by
have htrace := scalingTrace_invariant hn G hsym hG
refine ⟨?_,(htrace n).1.lower |> fun h => ?_⟩
· intro k i
by_cases hk : k<n
· change (if h : k<n then scaleUpdate hn G (scalingTrace hn G k) ⟨k,h⟩ else scalingTrace hn G k) i ≤ _
rw [dite_eq_left hk]
exact scaleUpdate_le hn G _ (htrace k).1 ⟨k,hk⟩ i
· simp [scalingTrace,hk]
· refine ⟨fun i => ⟨h i,(htrace n).1.upper i⟩,(htrace n).1.feasible,?_⟩
intro i
exact (htrace n).2 i i.isLt
def rowPeak {n : ℕ} (hn : 2 ≤ n) (g : Fin n → Fin n → ℚ) (i : Fin n) : ℚ :=
(univ.erase i).sup' (others_nonempty hn i) (g i)
def scaledHoleMatrix {n : ℕ} (g : Fin n → Fin n → ℚ) (v : Fin n → ℚ) (i j : Fin n) : ℚ :=
g i j/(v i*v j)
def BalancedRows {n : ℕ} (hn : 2 ≤ n) (g : Fin n → Fin n → ℚ) : Prop :=
∀ i, (1:ℚ)/4 ≤ rowPeak hn g i ∧ rowPeak hn g i ≤ 1
theorem one_pass_restores_balance {n : ℕ} (hn : 2 ≤ n) (g G : Fin n → Fin n → ℚ)
(hGsym : ∀ i j, G i j=G j i)
(hG : ∀ i j, i≠j → alpha ≤ G i j ∧ G i j ≤ 3)
(hpre : ∀ i, (1:ℚ)/8 ≤ rowPeak hn g i)
(haccuracy : ∀ i j, i≠j → g i j ≤ G i j ∧ G i j ≤ g i j+2*alpha) :
(∀ i, (1:ℚ)/16 ≤ scalingTrace hn G n i) ∧
BalancedRows hn (scaledHoleMatrix g (scalingTrace hn G n)) := by
let v := scalingTrace hn G n
have hv := (scalingTrace_invariant hn G hGsym hG n).1
have hlow (i : Fin n) : (1:ℚ)/16 ≤ v i := by
obtain ⟨j,hj,heq⟩ := Finset.exists_mem_eq_sup' (others_nonempty hn i) (g i)
have hji := (mem_erase.mp hj).1
change rowPeak hn g i=g i j at heq
have hgij : (1:ℚ)/8 ≤ g i j := by rw [← heq]; exact hpre i
have hGi := (haccuracy i j hji.symm).1
have hfeas := hv.feasible i j hji.symm
have hup := mul_le_mul_of_nonneg_left (hv.upper j) (hv.pos i).le
dsimp [v]
linarith
refine ⟨hlow,?_⟩
intro i
constructor
· obtain ⟨j,hji,heq⟩ := (one_pass_scaling hn G hGsym hG).2.2.2 i
have hprod : (1:ℚ)/256 ≤ v i*v j := by
calc
(1:ℚ)/256 = ((1:ℚ)/16)*((1:ℚ)/16) := by norm_num
_ ≤ v i*v j := mul_le_mul (hlow i) (hlow j) (by norm_num) (hv.pos i).le
have hacc := (haccuracy i j hji.symm).2
have hg : (1:ℚ)/4 ≤ scaledHoleMatrix g v i j := by
apply (le_div_iff₀ (mul_pos (hv.pos i) (hv.pos j))).mpr
change v i*v j=G i j at heq
norm_num [alpha] at hacc
nlinarith
apply hg.trans
exact Finset.le_sup' (scaledHoleMatrix g v i) (mem_erase.mpr ⟨hji,mem_univ _⟩)
· apply Finset.sup'_le
intro j hj
have hji := (mem_erase.mp hj).1
apply (div_le_one (mul_pos (hv.pos i) (hv.pos j))).mpr
exact ((haccuracy i j hji.symm).1).trans (hv.feasible i j hji.symm)
def sigma (D K : ℕ) (epsilon : ℚ) : ℚ := min (alpha/(100*D)) (epsilon/(1000*K))
def ratioEstimate (abar dbar : ℚ) : ℚ := if 0<abar then dbar/abar else 1
def upperEstimate (D : ℕ) (dbar zbar : ℚ) : ℚ :=
if 0<dbar then max alpha (min 3 ((D:ℚ)*zbar/dbar+alpha)) else 1
end MatchingFPRAS.Counting
end OAI