Demo: The 3-D Laplace equation: P₁ Finite Element

This demo program solves the 3-D Laplace equation using P₁ finite elements. For this end, it is clearly sufficient to recopy the first Laplace demo 1 program and replace the class Laplace2DT3 by Laplace3DT4. Of course we provide for this example a mesh file with a 3-D domain (a cube).