Fast differential elimination in C: The CDiffElim environment

Abstract

We introduce the CDiffElim environment, written in C, and an algorithm developed in this environment for simplifying systems of overdetermined partial differential equations by using differentiation and elimination. This environment has strategies for addressing difficulties encountered in differential elimination algorithms, such as exhaustion of computer memory due to intermediate expression swell, and failure to complete due to the massive number of calculations involved. These strategies include low-level memory management strategies and data representations that are tailored for efficient differential elimination algorithms. These strategies, which are coded in a low-level C implementation, seem much more difficult to implement in high-level general purpose computer algebra systems. A differential elimination algorithm written in this environment is applied to the determination of symmetry properties of classes of (n+1)-dimensional coupled nonlinear partial differential equations of form i u t+∇ 2 u +(a(t)| x | 2+ b (t)· x +c(t)+d| u | 4/n) u = 0 , where u is an m-component vector-valued function. The resulting systems of differential equations for the symmetries have been made available on the web, to be used as benchmark systems for other researchers. The new differential elimination algorithm in C, runs on the test suite an average of 400 times faster than our RifSimp algorithm in Maple. New algorithms, including an enhanced GCD algorithm, and a hybrid symbolic-numeric differential elimination algorithm, are also described.