,
Yuval Filmus
,
Ian Mertz
,
Alexander Smal
,
Antoine Vinciguerra
Creative Commons Attribution 4.0 International license
In a seminal work, Buhrman et al. (STOC 2014) defined the class CSPACE(s,c) of problems solvable in space s with an additional catalytic tape of size c, which is a tape whose initial content must be restored at the end of the computation. They showed that uniform TC¹ circuits are computable in catalytic logspace, i.e., CL = CSPACE(O(log{n}), 2^{O(log{n})}), thus giving strong evidence that catalytic space gives L strict additional power. Their study focuses on an arithmetic model called register programs, which has been a focal point in development since then.
Understanding CL remains a major open problem, as TC¹ remains the most powerful containment to date. In this work, we study the power of catalytic space and register programs to compute circuits of larger depth. Using register programs, we show that for every ε > 0,
SAC² ⊆ CSPACE (O((log²n)/(log log n)), 2^{O(log^{1+ε} n)}) .
On the other hand, we know that SAC² ⊆ TC² ⊆ CSPACE(O(log²{n}) , 2^{O(log{n})}). Our result thus shows an O(log log n) factor improvement on the free space needed to compute SAC², at the expense of a nearly-polynomial-sized catalytic tape.
We also exhibit non-trivial register programs for matrix powering, which is a further step towards showing NC² ⊆ CL.
@InProceedings{alekseev_et_al:LIPIcs.MFCS.2025.6,
author = {Alekseev, Yaroslav and Filmus, Yuval and Mertz, Ian and Smal, Alexander and Vinciguerra, Antoine},
title = {{Catalytic Computing and Register Programs Beyond Log-Depth}},
booktitle = {50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025)},
pages = {6:1--6:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-388-1},
ISSN = {1868-8969},
year = {2025},
volume = {345},
editor = {Gawrychowski, Pawe{\l} and Mazowiecki, Filip and Skrzypczak, Micha{\l}},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2025.6},
URN = {urn:nbn:de:0030-drops-241136},
doi = {10.4230/LIPIcs.MFCS.2025.6},
annote = {Keywords: catalytic computing, circuit classes, polynomial method}
}