DDSCAT.5a solves the problem of scattering and absorption by an array of polarizable point dipoles interacting with a monochromatic plane wave incident from infinity. DDSCAT.5a has the capability of automatically generating dipole array representations for a variety of target geometries (see §18) and can also accept dipole array representations of targets supplied by the user (although the dipoles must be located on a cubic lattice). The incident plane wave can have arbitrary elliptical polarization (see §20), and the target can be arbitrarily oriented relative to the incident radiation (see §16). The following quantities are calculated by DDSCAT.5a :
,
where 
is the absorption cross section;
,
where 
is the scattering cross section;
;
, defined so that the phase-lag
(in radians) of a plane wave after propagating a distance L is just
,
where 
is the number density of targets.
4 Mueller scattering intensity matrix 
describing the complete
scattering properties of the target for scattering directions specified
by the user.
(see §14).
(see §14).