Element Stiffness Matrix

The stiffness matrices are integrated numerically where the number of integration points is fixed for each element type by the parameter npts. The element has a number of dimensions defined by ndim. Suppose we have nel 2-D elements (ndim=2) for which the stiffness matrix has to be calculated, the following should be defined:

\[j = [{j11}_1, {j12}_1, {j21}_1, {j22}_1, ..., {j11}_{nel}, {j12}_{nel}, {j21}_{nel}, {j22}_{nel}]\]