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diff --git a/notes/35_current_results_consolidated.md b/notes/35_current_results_consolidated.md new file mode 100644 index 0000000..f22a0c1 --- /dev/null +++ b/notes/35_current_results_consolidated.md @@ -0,0 +1,149 @@ +# Current Results (Consolidated) + +Authoritative snapshot of where the project stands. Supersedes the framing in +`00_project_overview.md` and `03_paper_outline.md` (both stale: they still say +"redundancy-exhaustion **phase transition**" and omit the estimator). The +current, correct framing lives here and in notes 18, 24, 26, 29, 34. + +## Central claim + +> Random feedback imposes a quantifiable, **soft** (non-threshold) operator +> burden relative to BP that is present at every capacity margin (including +> overparameterized) and grows smoothly as capacity tightens. The static +> alignment geometry is exactly characterized (Beta law, prior-free minimax); +> the initial operator erosion is exactly the hidden-layer BP speed share; a +> closed-form spectral law turns that scalar burden into the finite-time gap and +> explains the soft ramp; and an early operator-velocity estimator predicts the +> finite-time FA/BP gap with no fit (corr 0.999). + +## The erosion ladder (organizing spine) + +All "burden" objects, as one ladder (note 24 is the through-line: *random +feedback induces a distribution of residual-direction operator erosion `e(r)`; +capacity controls that distribution; the finite-time gap is the product of the +tangent operators*): + +| level | object | status | role | +|---|---|---|---| +| 0 static geometry | `Q_l = cos^2(W^T,B) ~ Beta(1/2,(D-1)/2)` | exact | defines alignment | +| 1 null model | `e ~ Beta(k/2,(P-k)/2)`, `E[e]=k/P` | exact, **overpredicts** | proves nonzero cost for any `k>0` | +| 2 exact init | `e_0 = 1 - r^T S_FA r / r^T K_BP r`, `E_B[e_0]=hidden_share` | exact, validated | the real `t=0` burden; gives `rho=1-E_B[e_0]` | +| 3 finite time | closed form `gap_T(rho,{lam_i})` (note 34); estimator `K_t` (notes 15-17) | closed form: shape; estimator: magnitude | the actual gap | + +## Three contributions + +Refined to three pillars: 1 & 2 are foundational (static capacity geometry), +3 is an independent track (initialization optimality), and the rest of the +results build on 1 to form the main gap pillar, ordered as a progression +(exists & soft -> exact at init -> finite-time law -> validation). + +### Contribution 1 — Distributional capacity of random feedback (static geometry) + +*(old 1 + 2.)* + +- Exact static-alignment law `Q_l = cos^2(W_{l+1}^T, B_l) ~ Beta(1/2,(D_l-1)/2)`, + `E[Q]=1/D`, with log-volume capacity cost `C_l(q) = -log P(Q_l >= q)`. +- Multilayer scaling: independent blocks => `C_all = sum_l C_l = Theta(L n^2)`, + raw feasible volume `exp[-Theta(L n^2)]`. +- Role: defines and measures the feedback-alignment burden before training. +- **Proven.** `scripts/static_alignment_beta.py`, `scripts/capacity_scaling.py`. + +### Contribution 2 — Prior-free minimax optimality of random feedback + +*(old 3, independent track.)* + +- Without a prior on forward weights or task, no initialization beats isotropic + random feedback: `sup_mu inf_a E[(a^T b)^2] = 1/D`, achieved by isotropic. +- Role: self-contained -- the burden cannot be designed away at initialization. +- **Proven.** `scripts/minimax_initialization.py`. + +### Contribution 3 — The FA/BP operator gap: always nonzero, soft, exactly anchored at init, quantified over training + +*(old 4 + 5 + 6, as a four-level progression on Contribution 1.)* + +- **(a) Existence & softness.** `rho = output_share < 1` => `gap > 0` at every + `depth >= 2` and every capacity margin; analytic in the spectrum => smooth, + **no redundancy-exhaustion threshold** (null model `E[e]=k/P`, `P(e=0)=0`). +- **(b) Exact at t=0.** `E_B[e_0 | W,r] = hidden_share = 1 - ||g_out^BP||^2 / + sum_l ||g_l^BP||^2`; one-hidden-layer Gaussian feedback => full conditional + Gaussian. Supplies the scalar burden `rho = 1 - E_B[e_0]`. + **Proven + validated** (0.4378 vs 0.4403). `scripts/actual_fa_initial_operator_moments.py`. +- **(c) Finite-time law.** closed-form soft-ramp gap + `gap_T = (1/2N) sum_i c_i^2 [(1-eta rho lam_i/N)^{2T} - (1-eta lam_i/N)^{2T}]` + (mechanism + shape, `log gap ~ const - c rho lam_min`; note 34) **plus** the + early operator-velocity estimator `K_hat_t = K_0 + t(K_s-K_0)/s` + (drift-corrected magnitude, corr 0.999). closed form = why soft; estimator = how much. + `scripts/closed_form_soft_ramp.py`, `scripts/compressed_operator_predictor.py`. +- **(d) Empirical validation (no fit).** matrix-alignment Beta; e0 Gaussian; + soft ramp (smooth, nonzero at positive margin -> refutes phase transition); + estimator trajectory overlap. + +### Old numbering -> new + +```text +old 1, old 2 -> C1 +old 3 -> C2 +old 4 -> C3(b) +old 6 (closed form + estimator) -> C3(c) +old 5 -> C3(d) +(new) existence & soft -> C3(a) +``` + +## Key numbers (the evidence) + +- init moment: `E_B[e_0]=0.4378 +/- 0.008` vs theory `hidden_share=0.4403`. +- estimator: linear-velocity gap MAE `0.00189`, corr `0.99885` (256 traj); + stress grid corr `0.994-0.99989` across depth 1/2/3, width 32/64/96, + horizon 25/50/100 (notes 15-17). fixed `K(0)` is ~10x worse. +- soft ramp (dense `T=30000`): gap `0.147 -> 0.00016` smooth across margin + `-190 -> +130`, **nonzero at positive margin, no kink** (note 22). +- closed-form law (corrected, matched data/init -- note 37): no-fit + `corr(log pred, log measured)=0.933` (matched init) / `0.982` (5-init geo + mean); measured `log(gap)` linear in margin `R^2=0.993`; + `corr(lam_min_mean,-log gap)=0.987` (note 34+37; 0.977/0.963 retired). + +## Concise figure list (5 figures, one per contribution) + +1. static Beta histogram + QQ (sanity). +2. soft ramp: gap vs margin, log-y, smooth, nonzero at positive margin + (refutes phase transition). `outputs/phase_transition_dense_T30000_352traj/`. +3. init moment: `E_B[e_0]` vs `hidden_share`, no-fit scatter. + `outputs/actual_fa_initial_operator_moments/`. +4. **estimator: predicted vs empirical finite-time gap, 256 traj + stress + grid, corr 0.999 (centerpiece).** `outputs/compressed_operator_s20_256traj_T50_width64_plots/`. +5. **closed form vs measured ramp + ramp law.** + `outputs/closed_form_soft_ramp/closed_form_vs_measured_ramp.png`. + +## Proven vs estimated vs approximate + +- proven, no fit: contributions 1, 3; the `E[e]=k/P` null model; the init + moment `E_B[e_0]=hidden_share`. +- closed-form gap law (note 34): proven under lazy (A1) + scalar-erosion (A2); + captures shape, not magnitude. +- estimator: no fitted scalar, but **conditional on early operators `(K_0,K_s)`** + -- a predictive finite-time estimator, not an architecture-only theorem. + +## Open problem (the one real gap) + +Derive the drift / effective burden from architecture + initialization so the +finite-time gap becomes architecture-only: + +- predict `rho` (hence `hidden_share`) from infinite-width NTK recursions; +- predict the drift `K_s - K_0` (alignment gain) -- naive `dot_K_0` fails + (note 31), so use a bounded short-time alignment-gain path or a deep-linear / + two-layer order-parameter solution; +- a per-mode spectral erosion `rho_i` refining the scalar A2. + +## Superseded / cleanup + +- `00_project_overview.md`, `03_paper_outline.md`: stale framing; retire + "phase transition", add the estimator + closed-form law. +- notes 19-21 (transition-as-kink): refuted by the dense sweep (note 22). +- hard-`k` as a *gap predictor*: it overpredicts (note 25); keep only as the + null model that motivates the operator object. +- `scripts/actual_fa_initial_erosion_distribution.py` (e0 Gaussian, note 32): + the sampler reuses the analytic coefficient (partly circular) -- switch it to + the real FA backward (verified to reproduce the same numbers). +- `scripts/alignment_recovery_dynamics.py` (rho(t) recovery probe): superseded + by the estimator + closed-form law; keep only as an optional `t=0` sanity or + remove. |
