Vol. I · No. 1
Trust Propagation

The PaTAS Simulator — Parallel Trust Assessment, propagated through neural networks via Subjective Logic —

Ouattara et al.
Running Example
Input Trust Tx
Ts — size feature
Tnr — # rooms feature

Adjust input trust opinions; b + d + u is renormalized as you drag.

Parameter Trust Tθ
Tθ₁ — weight on s (=10)
Tθ₂ — weight on nr (=100)
Fusion Operator ⊕
Preset Scenarios

Apartment-rent perceptron with parallel Trust Nodes Network

y′ = θ₁ · s + θ₂ · nr   |   Ty′ = (Tθ₁ ⊗ Ts) ⊕ (Tθ₂ ⊗ Tnr)

Neural Network Trust Nodes Network (parallel) θ₁ = 10 θ₂ = 100 s → N₁ nr → N₂ N₃ → y′ ⇣ Trust propagation in parallel ⇣ Ts → Tnr → Tθ₁ ⊗ Ts Tθ₂ ⊗ Tnr TN s TN nr TN₃ ⊕ → Ty′

Step-by-step trace

Final output trust Ty′
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Trust (belief)
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Distrust
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Uncertainty
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Network Inputs x ∈ ℝ²
Tx₁
Tx₂
Parameter Trust Profile Tθ

All edges share one of these trust profiles; the architecture is 2 → 3 → 2.

IPTA Activation Mask ReLU

Pick which hidden neurons are activated for this specific inference. PaTAS' GenIPTA prunes the Trust Nodes Network to just the activated path.

Output Aggregation ⊕

Aggregates the two output-neuron trust opinions into a single consolidated network trust.

Trust Feedforward through a 2 → 3 → 2 network

Tz(l)i = ⋁j ( Tx(l-1)j ⊗ Tθ(l)ij )  ,  Tx(l+1) = Tf(Tz(l))

Trust Feedforward & IPTA trace

Aggregated Ty
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Trust
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Distrust
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Uncertainty
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Algorithm 1 — ParameterTrustUpdate(g, Ty, ϵ)

Walks one mini-batch through the six steps that revise the trust of a single parameter Tθi,j given gradient evidence, label trust, input-feature trust, and learning-rate trust. Pick a neuron, edit the gradients, then step through.

Batch Label Trust {Ty}

Click any bar to expand sliders and edit (b, d, u) directly. Ty_batch = ⋁y∈y_batch Ty (Line 4).

Target Neuron & Gradients N(i)

Edit gradients gi,j per incoming edge:

0.05

|gi,j| < ϵ → weak (positive evidence r); ≥ ϵ → strong (negative evidence s).

Auxiliary Trust Tlr, Tx
Tlr — learning rate
Txj — input feature
Initial Tθi,j (before update) prior
current parameter trust
Step 0 / 6

Network view: target parameter and its evidence

Tθi,j ← Update(Revise(Tθi,j, Tni‖Y), Tlr, Txj, Tybatch)

Line 3–4 · Step 1 Aggregate label trust over the mini-batch
Cumulative fusion of all Ty in the batch:
Tybatch = ⋁y∈ybatch Ty
Result: —
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Line 8 · Step 2 Gather gradients for the target neuron
gi(l) = { gi,j(l) | j ∈ N(i) }
Gradients for —: —
Line 10 · Step 3 NodeTrust — quantify gradient evidence
Count weak/strong gradients via ϵ, then apply Baseline-Prior Quantification (W = 2):
b = r/(W+r+s),   d = s/(W+r+s),   u = W/(W+r+s)
—
Result: —  (Tni|ybatch)
Line 12 · Step 4 DeduceTrust — combine conditionals over Tybatch
Tni|ȳbatch is set vacuous (0, 0, 1). Then apply the deduction operator ⊚:
Tni‖Ybatch = Tybatch ⊚ ( Tni|ybatch, Tni|ȳbatch )
Result: —
Line 14–15 · Step 5 Revise — fuse deduced neuron trust into Tθ
Tθi,j ← Tθi,j ⊖ Tni‖Ybatch  (⊖ = cumulative fusion)
Before: —
After:   —
Line 16–17 · Step 6 Update — multiply by (Txj ⊘ Tybatch)
Conservative division ⊘ takes min belief, max disbelief:
(b, d, u) = (min(b₁,b₂), max(d₁,d₂), 1−(b+d))
Txj ⊘ Tybatch = —
Tθi,j ← Tθi,j ⊙ (Txj ⊘ Tybatch)
Final: —
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Net change: ΔTθi,j
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Δ trust
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Δ distrust
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Δ uncertainty
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Theorem 2 — Vacuous input ⇒ Vacuous output

If Tx = (0, 0, 1), then for any parameter trust profile Tθ, the PaTAS feedforward yields Ty′ = (0, 0, 1). The simulator empirically verifies this below. Re-roll random parameter trust to see it hold.

Theorem 3 — Symmetric inputs ⇒ Symmetric outputs

Given Tx = (b, d, u) and its symmetric counterpart Tx̄ = (d, b, u), the outputs satisfy by = dȳ, dy = bȳ, uy = uȳ. Also: full trust ⇒ dy = 0, full distrust ⇒ by = 0.

Convergence Sanity (Trust mass under repeated Averaging fusion)

Cumulative fusion of n independent identical opinions concentrates trust by reducing uncertainty. This mirrors what PaTAS does across a batch when label-trust evidence accumulates. Try varying n and the per-source opinion.

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Implementation notes: Trust discounting uses ωθ ⊗ ωx = (P·bx, P·dx, 1 − P(bx+dx)) with P = bθ + a·uθ. Cumulative fusion follows Jøsang's standard formulation; for the u=0 boundary an ε-stabilization is applied. The Parameter-Trust Update implements Algorithm 1 of the paper directly: Baseline-Prior Quantification (W=2) maps gradient counts to a binomial opinion, deduction ⊚ uses the binomial projection, revision ⊖ is realized as cumulative fusion (per Theorem 4 of the paper), and the auxiliary Update step composes binomial multiplication ⊙ with conservative division ⊘. Tlr enters via a final trust-discounting step that modulates the parameter trust by learning-rate reliability. Base rate a = 0.5 throughout. All numbers are recomputed live as inputs change.