Extremals of a left-invariant sub-Finsler metric on the Engel group

Abstract

The authors found extremals of arbitrary left-invariant sub-Finsler metric on the Engel group defined by a distribution of rank two. They use for this the Pontryagin Maximum Principle for the corresponding time-optimal problem in coordinates of the first kind. The obtained results are applied to the case of left-invariant sub-Riemannian metric with the same distribution.