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feat: polymerFreeEnergy < log 2 under (1+t)^|E| < 2 (§18.4 sharpening, Issue #1499) - #1524

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feat: polymerFreeEnergy < log 2 under (1+t)^|E| < 2 (§18.4 sharpening, Issue #1499)#1524
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@phasetr phasetr commented May 2, 2026

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Part of #1499.

phasetr and others added 2 commits May 3, 2026 03:51
…, Issue #1499)

Empty start. Convergence-regime upper bound polymerFreeEnergy < log 2.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
…, Issue #1499)

Add `polymerFreeEnergy_lt_log_two_of_pow_lt_two`: in the cluster-
expansion convergence regime `(1+t)^|E| < 2` (where the log Taylor
expansion converges via PR #1517), the polymer free energy is
strictly less than log 2.

Proof: combines `polymerFreeEnergy = log(1 + ε(t))` with
`ε(t) ≤ (1+t)^|E| - 1 < 1`, giving `1 + ε < 2` and applying
`Real.log_lt_log_iff`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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phasetr marked this pull request as ready for review May 2, 2026 18:53
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phasetr merged commit 17f0cd8 into main May 2, 2026
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phasetr deleted the feat/polymer-free-energy-lt-log-two branch May 2, 2026 18:55
phasetr added a commit that referenced this pull request May 2, 2026
…(§18.4 capstone, Issue #1499)

Add `freeEnergy_lt_log_two_plus_high_temp_correction`: under
`0 ≤ β·J`, `0 < |ι|`, and `(1+tanh(β·J))^|E| < 2`,
  freeEnergy G ⟨J, 0, β⟩ <
    log 2 + (|E|/|ι|) · log cosh(β·J) + log 2 / |ι|.

Combines `freeEnergy_eq_polymerFreeEnergy` (Step 612) with the strict
bound `polymerFreeEnergy < log 2` (PR #1524). Lifts the polymer-level
sharpening to the actual Ising free energy in the cluster-expansion
convergence regime.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
phasetr added a commit that referenced this pull request May 2, 2026
…(§18.4 capstone, Issue #1499) (#1527)

* feat: freeEnergy upper bound in cluster-expansion convergence regime (§18.4 capstone, Issue #1499)

Empty start. freeEnergy ≤ log 2 + |E|/|ι| log cosh + log 2 / |ι| under (1+tanh)^|E| < 2.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* feat: freeEnergy upper bound in cluster-expansion convergence regime (§18.4 capstone, Issue #1499)

Add `freeEnergy_lt_log_two_plus_high_temp_correction`: under
`0 ≤ β·J`, `0 < |ι|`, and `(1+tanh(β·J))^|E| < 2`,
  freeEnergy G ⟨J, 0, β⟩ <
    log 2 + (|E|/|ι|) · log cosh(β·J) + log 2 / |ι|.

Combines `freeEnergy_eq_polymerFreeEnergy` (Step 612) with the strict
bound `polymerFreeEnergy < log 2` (PR #1524). Lifts the polymer-level
sharpening to the actual Ising free energy in the cluster-expansion
convergence regime.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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