  Active galactic nuclei (AGNs) and quasars are important astrophysical objects
to understand. Recently, microlensing observations have constrained the size of
the quasar X-ray emission region to be of the order of 10 gravitational radii
of the central supermassive black hole. For distances within a few
gravitational radii, light paths are strongly bent by the strong gravity field
of the central black hole. If the central black hole has nonzero angular
momentum (spin), a photon's polarization plane will be rotated by the
gravitational Faraday effect. The observed X-ray flux and polarization will
then be influenced significantly by the strong gravity field near the source.
Consequently, linear gravitational lensing theory is inadequate for such
extreme circumstances. We present simple algorithms computing strong lensing
effects of Kerr black holes, including effects on polarization. Our algorithms
are realized in a program "KERTAP" in two versions: MATLAB and Python. The key
ingredients of KERTAP are: a graphic user interface, a {\it backward}
ray-tracing algorithm, a polarization propagator dealing with gravitational
Faraday rotation, and algorithms computing observables such as flux
magnification and polarization angles. Our algorithms can be easily realized in
other programming languages such as FORTRAN, C, and C++. The MATLAB version of
KERTAP is parallelized using the MATLAB Parallel Computing Toolbox and the
Distributed Computing Server. The Python code was sped up using Cython and
supports full implementation of MPI using 'mpi4py' package. As an example, we
investigate the inclination angle dependence of the observed polarization and
the strong lensing magnification of AGN X-ray emission. We conclude that it is
possible to perform complex numerical-relativity-related computations using
interpreted languages such as MATLAB and Python.
