add a fast likelihood function

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.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/misc.h b/src/misc.h
index c93afba..eb62e46 100644
--- a/src/misc.h
+++ b/src/misc.h
@@ -3,6 +3,9 @@
 
 #include <stdlib.h> /* for size_t */
 
+#define LNFACT_MAX 100
+
+double lnfact(unsigned int n);
 double kahan_sum(double *x, size_t n);
 double interp1d(double x, double *xp, double *yp, size_t n);
 int isclose(double a, double b, double rel_tol, double abs_tol);