Glossary¶

Domain-specific terms used throughout SC-NeuroCore documentation.

Stochastic Computing¶

Term	Definition
Bitstream	Temporal sequence of {0,1} bits where the proportion of 1s encodes a probability p ∈ [0,1].
Bitstream length (L)	Number of bits in a stochastic bitstream. Precision scales as O(1/√L).
Unipolar SC	Bitstream encodes values in [0,1]. Multiplication via AND gate.
Bipolar SC	Bitstream encodes values in [-1,1] via p=(x+1)/2. Multiplication via XNOR gate.
Popcount	Count of 1-bits in a packed word. Used to decode bitstream probability.
CORDIV	Stochastic division circuit (Li et al. 2014). Sequential state machine: x=1→z=1, y=1→z=0, else hold.
MUX	2:1 multiplexer for scaled addition: z = s·x + (1-s)·y.
LFSR	Linear Feedback Shift Register. Pseudo-random number generator for bitstream encoding.
Sobol sequence	Low-discrepancy quasi-random sequence. Gives O(1/L) convergence vs O(1/√L) for Bernoulli.
Decorrelation	Requirement that bitstreams use independent random sources. Correlated inputs bias results.
Q8.8	Signed fixed-point format: 8 integer bits + 8 fractional bits. Range [-128, +127.996], step 1/256.
SC-aware pruning	Remove weights whose bitstream contribution falls below noise floor at target L.

Term	Definition
LIF	Leaky Integrate-and-Fire neuron. τ_m dV/dt = -(V-V_rest) + R·I. Spike when V > V_th.
Izhikevich	Two-variable neuron model: dv/dt = 0.04v² + 5v + 140 - u + I. 20+ firing patterns.
Hodgkin-Huxley	Biophysical neuron with Na⁺/K⁺ ion channel gating (1952 Nobel Prize model).
AdEx	Adaptive Exponential integrate-and-fire. LIF + exponential spike initiation + adaptation.
FitzHugh-Nagumo	Reduced 2-variable model: fast voltage + slow recovery. Limit cycle dynamics.
Hindmarsh-Rose	3-variable bursting model with slow modulation variable z.
Surrogate gradient	Smooth approximation of the Heaviside spike function for backpropagation (FastSigmoid, ATan).
STDP	Spike-Timing-Dependent Plasticity. Pre-before-post → potentiation. Post-before-pre → depression.
STP	Short-Term Plasticity. Facilitation (repeated spikes increase release) or depression (vesicle depletion).
E-prop	Eligibility propagation. Three-factor rule: pre × post × error. Online credit assignment.
R-STDP	Reward-modulated STDP. Eligibility traces gated by global reward signal.
BCM	Bienenstock-Cooper-Munro rule. Sliding threshold metaplasticity.
Population	Group of identical neurons managed as a unit.
Projection	Synaptic connectivity between populations. Stored as CSR sparse matrix.
CSR	Compressed Sparse Row format: (indptr, indices, data) arrays for sparse matrices.
Spike gating	Skip idle neurons during simulation. Compute ∝ active count.

Term	Definition
LUT	Look-Up Table. Basic FPGA logic element. One LIF neuron ≈ 30–50 LUTs.
FF	Flip-Flop. 1-bit register on FPGA.
DSP48	Dedicated multiply-accumulate block on Xilinx FPGAs.
BRAM	Block RAM. On-chip memory for weight storage.
Yosys	Open-source FPGA synthesis tool. SC-NeuroCore uses it for ice40/ECP5.
Vivado	Xilinx FPGA synthesis and implementation tool. For Artix-7/Zynq.
AER	Address-Event Representation. Spike encoding: (neuron_id, timestamp) pairs.
Event-driven	Neurons compute only on input events. Power ∝ spike rate, not clock rate.
Clock-driven	Every neuron updates every clock cycle. Power ∝ N × f_clk.
SymbiYosys	Formal verification frontend for Yosys. Proves assertions via SMT solvers.
SystemVerilog	Hardware description language. SC-NeuroCore's equation compiler emits this.

Term	Definition
SCPN	Stochastic Computational Phase Network. 16-layer hierarchical oscillator model.
K_nm	Inter-layer coupling matrix. Symmetric, zero-diagonal, calibrated to PhysioNet PLV (r=0.951).
Ω_N	Natural frequencies for 16 SCPN layers. L2 ≈ 40 Hz (gamma), L5 ≈ 1 Hz (intentional).
Kuramoto model	Coupled oscillator model: dθ/dt = ω + Σ K sin(Δθ). Phase synchronisation.
Order parameter R	Kuramoto coherence: R =
BKT transition	Berezinskii-Kosterlitz-Thouless. Topological phase transition via vortex unbinding.
FIM	Fisher Information Metric. Self-observation feedback: ΔW -= λ·(activity-μ)/N.
Φ	Integrated information (Tononi IIT). Measures how much a system is "more than its parts."
Sheaf defect	Obstruction to global phase coherence. Zero when synchronised.
Winding number	Topological invariant counting phase wraps around S¹.
Ricci curvature	Ollivier-Ricci curvature on graphs. Positive = community, negative = bottleneck.
Lazarus protocol	Checkpoint save/load/merge for identity substrate. Preserves weights + voltages + traces.

Term	Definition
NIR	Neuromorphic Intermediate Representation. Framework-agnostic SNN graph format.
Norse	PyTorch-based SNN library (Denmark). LIF/LI neurons with autograd.
snnTorch	PyTorch SNN library (Eshraghian, UCSC). Leaky/Synaptic neurons.
SpikingJelly	Chinese SNN framework. Event-driven training.
Brian2	Python SNN simulator (Goodman, Brette). ODE-based, C++ codegen.
Lava	Intel's neuromorphic framework for Loihi chips.
SpiNNaker	Manchester ARM-based neuromorphic platform.