In this video, the basis functions that are not so clean in the description as other basis functions are discussed. The space-filling element shapes such as triangles and tetrahedrons, also called simplex elements, are discussed here.
Continuing from the previous video, the basis function is written, and the shape of this function is shown. We see that simplex elements are simpler than quadrilaterals and hexahedral elements. Three Dimensional tetrahedral elements are discussed. It is seen that the simplex elements have constant gradients. Finally, integrating these functions is discussed.