F. J. Gaspar,  C. Rodrigo & E. Heidenreich. (1970). Geometric Multigrid Methods on Structured Triangular Grids for Incompressible Navier-Stokes Equations at Low Reynolds Numbers.
            <i>International Journal of Numerical Analysis and Modeling</i>. <i>11</i> (2).
            400-411.
         doi: