r/AskComputerScience • u/Upset-Opinion-4997 • 23h ago
How does the condition-number barrier affect real-world sparse optimization algorithms (paper)?
I was reading about sparse least-squares solvers and came across this paper at http://arxiv.org/abs/2608.02588v1. The abstract claims a lower bound: even for randomized poly-time algorithms, you can’t beat a linear dependence on the restricted condition number $κ_{s+k}$ when trading off sparsity and error tolerance. That feels like it has teeth, but I'm not sure how it maps to practice.
What I'm confused about
In the real world, practitioners often heuristic-sparsify models (e.g., feature selection in ML, compressed sensing) or use iterative hard thresholding. Does this lower bound mean those methods are *fundamentally* limited, or does the result rely on assumptions that don't hold in typical use cases? The paper conditions on a variant of the Small-Set Expansion Hypothesis, which is a complexity-theoretic assumption but not something engineers usually worry about.
Tradeoffs in the proof
The authors mention using an automated Gemini-based agent system to first construct the proof. That part fascinates me, but my CS theory chops are too weak to judge whether the reduction itself (from a graph hypothesis to a linear algebra problem) preserves practical relevance. The result holds even on rational instances with full-rank matrices, so the hardness doesn't hinge on numerical pathologies. Yet I haven't seen this cited in any applied optimization forums yet.
Has anyone implemented sparse regression workflows where the condition number $κ$ scales steeply with problem size? If so, does this paper suggest a fundamental ceiling on how well approximate methods can perform, or is there wiggle room in relaxing the hardness hypothesis? I’m curious whether this is more of a theoretical boundary condition or something that bites practitioners in the wild.
Also, the proof relied on automation. Are there follow-up efforts to formalize or verify the result independently (e.g., in Lean or Isar)? That feels like a separate discussion.