**2.4 LIBEM2 and L2LC modules, test problem and results**

This section includes an outline of the Laplace interior BEM 2D (LIBEM2) and Laplace 2D linear boundary approximation constant element (L2LC) modules, and they are demonstrated by means of a test problem. The LIBEM2 module solves Laplace's equation in an interior two-dimensional domain. L2LC is the most important component module.

**L2LC.** The L2LC module computes the discrete Laplace operators for twodimensional problems. In the notation of this article, the routine computes f g *Le <sup>Δ</sup>*<sup>~</sup> *Sj* ð Þ *p* , f g *Me <sup>Δ</sup>*<sup>~</sup> *Sj* ð Þ *<sup>p</sup> , M<sup>t</sup>* f g*<sup>e</sup> <sup>Δ</sup>*<sup>~</sup> *Sj* ð Þ *p* and f g *Ne <sup>Δ</sup>*<sup>~</sup> *Sj* ð Þ *p* , where *ΔS* e*<sup>j</sup>* is the panel that is the domain of integration and *p* is any point. The call to the subroutine has the following form:
