Lower bounds for algebraic machines, semantically

Luc Pellissier (1) , Thomas Seiller (2, 3)

1 LACL - Laboratoire d'Algorithmique Complexité et Logique
2 CNRS - Centre National de la Recherche Scientifique
3 LIPN - Laboratoire d'Informatique de Paris-Nord

This paper presents a new semantic method for proving lower bounds in computational complexity. We use it to prove that maxflow, a PTIME complete problem, is not computable in polylogarithmic time on parallel random access machines (PRAMs) working with integers, showing that NCZ \neq PTIME, where NCZ is the complexity class defined by such machines, and PTIME is the standard class of polynomial time computable problems (on, say, a Turing machine). On top of showing this new separation result, we show our method captures previous lower bounds results from the literature: Steele and Yao’s lower bounds for algebraic decision trees, Ben-Or’s lower bounds for algebraic computation trees, Cucker’s proof that NC is not equal to PTIME on the reals, and Mulmuley’s lower bounds for “PRAMs without bit operations”.

Domaines: Complexité [cs.CC]; Logique en informatique [cs.LO]; Géométrie algébrique [math.AG]; Systèmes dynamiques [math.DS]; Calcul parallèle, distribué et partagé [cs.DC]; Théorie et langage formel [cs.FL]

Luc Pellissier, Thomas Seiller. Lower bounds for algebraic machines, semantically. 2021. ⟨hal-02487667v2⟩