A new method for computing self-gravity in an isolated system
  A new approximation method for inverting the Poisson's equation is presented
for a continuously distributed and finite-sized source in an unbound domain.
The advantage of this image multipole method arises from its ability to place
the computational error close to the computational domain boundary, making the
source region almost error free. It is contrasted to the modified Green's
function method that has small but finite errors in the source region.
Moreover, this approximation method also has a systematic way to greatly reduce
the errors at the expense of somewhat greater computational efforts. Numerical
examples of three-dimensional and two-dimensional cases are given to illustrate
the advantage of the new method.
