bim1c_elem_to_nodes
                 Compute interpolated values at nodes u_nod given values at element mid-points u_el.
 If called with more than one output, also return the interpolation matrix m_el such that
 u_nod = m_el * u_el.
 If repeatedly performing interpolation on the same mesh the matrix m_el obtained by a previous call 
 to bim1c_elem_to_nodes may be passed as input to avoid unnecessary computations.
Source Code: bim1c_elem_to_nodes