bim2c_tri_to_nodes
                 Compute interpolated values at triangle nodes u_nod given values at triangle mid-points u_tri.
 If called with more than one output, also return the interpolation matrix m_tri such that
 u_nod = m_tri * u_tri.
 If repeatedly performing interpolation on the same mesh the matrix m_tri obtained by a previous call 
 to bim2c_tri_to_nodes may be passed as input to avoid unnecessary computations.
Source Code: bim2c_tri_to_nodes