(click-drag the dielectric)
Poisson v4.0 calculates electrostatic potentials by numerically solving Poisson's equation in the presence of spherical and rectangular conductors, charge densities, and dielectrics. The gradient of this potential is then calculated in order to display the electric field and the divergence is calculated to display the induced charge. Although Poisson may be used in interactive mode using a click and drag metaphor, it is designed to be scripted. Many options, such as dielectrics, are only available through script.
Since potential, charge, and dielectric values are only defined on the grid points, it is advisable to use as small a grid as possible. There may be a mismatch between the on-screen drawing and the underlying grid if the grid is too coarse. This mismatch is most noticeable for bound charge.