/**
\addtogroup lalpulsar_hough
\brief Routines implementing the Hough-transform as a search-method for unknown pulsars.
\author Alicia M. Sintes, M. Alessandra Papa., Krishnan, B.

The  hierarchical Hough transform search strategy is
an efficient and highly parallel computer algorithm
\cite Schutz1999 , \cite Papa2001 .
This package provides the necessary routines for the Hough incoherent search
(the second stage of the search) to track the frequency evolution of
peaks in the spectra, which is known in advance for some choice of the
source parameters.

<i>The Hough transform</i> is  a transformation
between the data and the space of parameters that describe the signal.

\par Input:
Set of points in time-frequency plane that have been obtained
from the demodulated FT.
The demodulation  has been performed with respect to a certain sky
location and certain spin-down parameters,
in such a way  that, if a source was located in
the center of the patch and having the same spin-down parameters
for which it has been
demodulated, we will observe a set of points forming a horizontal
line at the intrinsic frequency  of the source \f$f_0\f$.
Due to the mismatch between the source  parameters
and the demodulated parameters we will observe a certain pattern in the time
frequency diagram following the<i>Hough transform master equation</i>.

\par Output:
Histograms in the parameter space:
for each \f$f_0\f$, residual spin-down and refined sky location.

The principle is the following: for every point in the <i>time-frequency</i>
plane, we enhance the number count in the  histogram in the pixels
that are <i>consistent</i>. At the end of this procedure, significant
clustering in a pixel in parameter space indicates likelihood of the
data containing a signal having the parameters of that pixel.

The package  is organized under the modules
\ref LUT_h, \ref PHMD_h, \ref HoughMap_h, \ref LALHough_h and
the files \ref PatchGrid.c, \ref Stereographic.c, \ref ParamPLUT.c, \ref NDParamPLUT.c,
\ref ConstructPLUT.c, \ref Peak2PHMD.c, \ref HoughMap.c, and \ref DriveHough.c.

\par Acknowledgment:
The authors thank S. Frasca and  C. Palomba for helpful discussions,
F. Massaioli for helping in the initial stages of code development,
and B. Allen and J. Creighton for their valuable implementation advice.
*/
