Electric field vectors of a dipole. The dipole is located at the center of the finest grid and is shown schematically by the red and blue circles. The modified convolution method is applied to construct the field (see Fig. 13 for comparison with the original method). The top panel presents the case of two nested grids, while the bottom panel corresponds to three nested grids. The black squares identify the grid interfaces. Note that the field is present and continuous across all nested grids Ω¹, Ω² and Ω³.