  DDSCAT 6.1 is a software package which applies the discrete dipole
approximation (DDA) to calculate scattering and absorption of electromagnetic
waves by targets with arbitrary geometries and complex refractive index. DDSCAT
6.1 allows accurate calculations of electromagnetic scattering from targets
with size parameters 2 pi a_eff/lambda < 15 provided the refractive index m is
not large compared to unity (|m-1| < 2). DDSCAT 6.1 includes support for MPI
and FFTW. We also make available a "plain" distribution of DDSCAT 6.1 that does
not include support for MPI, FFTW, or netCDF, but is much simpler to install
than the full distribution.
  The DDSCAT package is written in Fortran and is highly portable. The program
supports calculations for a variety of target geometries (e.g., ellipsoids,
regular tetrahedra, rectangular solids, finite cylinders, hexagonal prisms,
etc.). Target materials may be both inhomogeneous and anisotropic. It is
straightforward for the user to import arbitrary target geometries into the
code, and relatively straightforward to add new target generation capability to
the package. DDSCAT automatically calculates total cross sections for
absorption and scattering and selected elements of the Mueller scattering
intensity matrix for specified orientation of the target relative to the
incident wave, and for specified scattering directions.
