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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.
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This commit updates the charge spectrum initialization to convolve the charge
distribution over a wider range to make sure that we have a nonzero probability
of observing charges all the way down to qlo.
The reason for this is that previously for some negative charges the
probability of observing that charge was zero, which was causing the likelihood
to return nan.
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This commit updates get_event() to flag PMT charges below qlo, which is the
minimum charge value that we compute the charge PDFs for. This is to prevent
the likelihood from returning nan.
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Also, call this function when computing the psi parameter in nll_best().
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This commit updates the charge likelihood calculation to calculate:
P(hit,q|n) = P(q|hit,n)*P(hit|n)
This has almost no effect on the fit results, but is technically correct.
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This commit adds lots of comments to sno_charge.c and makes a couple of other
changes:
- use interp1d() instead of the GSL interpolation routines
- increase MAX_PE to 100
I increased MAX_PE because I determined that it had a rather large impact on
the likelihood function for 500 MeV electrons. This unfortunately slows down
the initialization by a lot. I think I could speed this up by convolving the
single PE charge distribution with a gaussian *before* convolving the charge
distributions to compute the charge distributions for multiple PE.
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This commit makes sure that when we conolve the single PE charge distribution
with a gaussian we integrate starting at zero since the PDF is zero for q < 0.
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This commit adds a fast function to calculate the expected number of PE at a
PMT without numerically integrating over the track. This calculation is *much*
faster than integrating over the track (~30 ms compared to several seconds) and
so we use it during the "quick" minimization phase of the fit to quickly find
the best position.
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This commit fixes a bug in the charge PDF calculation for n > MAX_PE. The
standard deviation should scale like sqrt(n)*qstd where qstd is the standard
deviation of the single PE charge distribution.
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