Mathematical Problems in Engineering
Volume 8 (2002), Issue 6, Pages 517-539

Eigenstructure of the equilateral triangle, Part II: The Neumann problem

Brian J. McCartin

Applied Mathematics, Kettering University, 1700 West Third Avenue, Flint 48504-4898, Michigan, USA

Copyright © 2002 Brian J. McCartin. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Lame's formulas for the eigenvalues and eigenfunctions of the Laplacian with Neumann boundary conditions on an equilateral triangle are derived using direct elementary mathematical techniques. They are shown to form a complete orthonormal system. Various properties of the spectrum and nodal lines are explored. Implications for related geometries are considered.