VPSPACE and a Transfer Theorem over the Reals

Abstract

We introduce a new class VPSPACE of families of polynomials. Roughly speaking, a family of polynomials is in VPSPACE if its coefficients can be computed in polynomial space. Our main theorem is that if (uniform, constant-free) VPSPACE families can be evaluated efficiently then the class $$\sf {PAR}_{\mathbb {R}}$$of decision problems that can be solved in parallel polynomial time over the real numbers collapses to $$\sf{P}_{\mathbb {R}}$$. As a result, one must first be able to show that there are VPSPACE families which are hard to evaluate in order to separate $$\sf{P}_{\mathbb {R}}$$from $$\sf{NP}_{\mathbb {R}}$$, or even from $$\sf{PAR}_{\mathbb {R}}$$.