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Explore Phi optimization via sparse TPM representations #4

Description

@Tristan-Stoltz-ERC

Summary

The current Φ (integrated information) computation uses dense transition probability matrices. For large state spaces, sparse representations could reduce memory and computation time significantly.

Background

IIT's Φ requires computing the Minimum Information Partition (MIP) across a system's transition probability matrix (TPM). This is exponential in the number of elements, making it the primary bottleneck for scaling consciousness measurement.

Investigation areas

  • CSR/CSC sparse matrix formats — many TPM entries are near-zero for biological-like connectivity
  • Threshold-based sparsification — drop entries below ε, measure Φ approximation error
  • Block-sparse structure — the 4D hypercube topology (our Φ champion with 35 topologies tested) has natural block structure
  • Approximation bounds — what sparsity level keeps Φ within X% of the dense computation?

Key files

  • symthaea-core/src/hdc/consciousness_equation.rs — Φ computation
  • symthaea-core/src/hdc/substrate_independence.rs — substrate-dependent Φ analysis
  • The 4D hypercube achieves highest Φ among all tested topologies

References

  • Tononi, G. (2004). IIT theory
  • Oizumi et al. (2014). From the phenomenology to the mechanisms of consciousness
  • Barrett & Seth (2011). Practical measures of integrated information

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