add a couple of improvements to the quad fitter and fix a bug in get_hough_transform()

This commit adds two improvements to the quad fitter:

1. I updated quad to weight the random PMT hit selection by the probability
that the PMT hit is a multiphoton hit. The idea here is that we really only
want to sample direct light and for high energy events the reflected and
scattered light is usually single photon.

2. I added an option to quad to only use points in the quad cloud which are
below a given quantile of t0. The idea here is that for particles like muons
which travel more than a few centimeters in the detector the quad cloud usually
looks like the whole track. Since we want the QUAD fitter to find the position
of the *start* of the track we select only those quad cloud points with an
early time so the position is closer to the position of the start of the track.

Also, I fixed a major bug in get_hough_transform() in which I was using the
wrong index variable when checking if a PMT was not flagged, a normal PMT, and
was hit. This was causing the algorithm to completely miss finding more than
one ring while I was testing it.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/random.h b/src/random.h
index dac48f8..747cfeb 100644
--- a/src/random.h
+++ b/src/random.h
@@ -18,8 +18,10 @@
 #define RANDOM_H
 
 #include "mt19937ar.h"
+#include <stdlib.h> /* for size_t */
 
 double randn(void);
 void rand_sphere(double *dir);
+void ran_choose_weighted(int *dest, double *w, size_t k, int *src, size_t n);
 
 #endif