T matrix code for scattering by homogeneous particles with discrete symmetries

Version 5.2

Michael Kahnert

Short description
Tsym (pronounced "tee-simm") solves the electromagnetic scattering problem by use of Waterman's 
T-matrix method (also known as the extended boundary condition or null-field method).
For particle morphologies with geometric symmetries, the code makes use of group theory to 
systematically simplify the numerical solution to Maxwell's equations. Although the code can, 
in principle, handle arbitrary star-shaped geometries, the code is most efficient for 
non-axisymmetric particles with finite symmetries.
For particles with small-scale surface roughness, the code also has an option to use an 
iterative Lippmann-Schwinger equation approach for computing the T matrix.
Main strength of the code: Increased numerical stability and reduced CPU time requirements 
for particles with geometric symmetries.
Main weakness of the code: The program does not contain any automatic convergence routines. 
Ensuring the convergence and correctness of the results is entirely the user's responsibility. 
Thus, it is recommended that the code be used by experienced users only.

User's guide
A description of the code can be found in the following paper:
M. Kahnert. The T-matrix code Tsym for homogenous dielectric particles with finite symmetries. 
J. Quant. Spectrosc. Radiat. Transfer 123 (2013) 62-78.

Acknowledgements
Tsym is making use of various subroutines for orientation-averaging, computation of Bessel 
functions, associated Legendre functions, vector coupling coefficients, and much more that 
have been borrowed from other codes. I am especially indebted to Heikki Laitinen, Kari Lumme, 
Dan Mackowski, Michael Mishchenko, Karri Muinonen, and Timo Nousiainen for their kind permission 
to include various Fortran routines from their respective programs in the distribution of Tsym. 
A detailed list of those subroutines and their authors can be found both in the comments of the 
source code and in the code documentation. The development of the code has been financed over 
the years in different projects financed by the Norwegian Research Council (Norsk forskningsråd) 
and by the Swedish Research Council (Vetenskapsrådet).