R_stiff: Compute the stiffness matrix
Description
Only executed when smooth.FEM.basis is run with the option CPP_CODE = FALSE. It computes the stifness matrix. The element (i,j) of this matrix contains the integral over the domain of the scalar product between the gradient of the ith and kth element
of the Finite Element basis. As common practise in Finite Element Analysis, this quantities are computed iterating over all the mesh triangles.Value
- A square matrix with the integrals of all the basis functions' gradients pairwise dot products.
The dimension of the matrix is equal to the number of the nodes of the mesh.