add some comments and divide by the density

2 files changed, 26 insertions, 6 deletions

diff --git a/muon.c b/muon.c
index ab79666..e225526 100644
--- a/muon.c
+++ b/muon.c
@@ -132,23 +132,43 @@ err:
     return -1;
 }
 
-double get_range(double T)
+double get_range(double T, double rho)
 {
+    /* Returns the approximate range a muon with kinetic energy `T` will travel
+     * in water before losing all of its energy. This range is interpolated
+     * based on data from the PDG which uses the continuous slowing down
+     * approximation.
+     *
+     * `T` should be in MeV, and `rho` should be in g/cm^3.
+     *
+     * Return value is in cm.
+     *
+     * See http://pdg.lbl.gov/2018/AtomicNuclearProperties/adndt.pdf. */
     if (!initialized) {
         if (init()) {
             exit(1);
         }
     }
 
-    return gsl_spline_eval(spline_range, T, acc_range);
+    return gsl_spline_eval(spline_range, T, acc_range)/rho;
 }
-double get_dEdx(double T)
+
+double get_dEdx(double T, double rho)
 {
+    /* Returns the approximate dE/dx for a muon in water with kinetic energy
+     * `T`.
+     *
+     *
+     * `T` should be in MeV and `rho` in g/cm^3.
+     *
+     * Return value is in MeV/cm.
+     *
+     * See http://pdg.lbl.gov/2018/AtomicNuclearProperties/adndt.pdf. */
     if (!initialized) {
         if (init()) {
             exit(1);
         }
     }
 
-    return gsl_spline_eval(spline_dEdx, T, acc_dEdx);
+    return gsl_spline_eval(spline_dEdx, T, acc_dEdx)/rho;
 }
diff --git a/muon.h b/muon.h
index bc7f03e..461339b 100644
--- a/muon.h
+++ b/muon.h
@@ -1,7 +1,7 @@
 #ifndef MUON_H
 #define MUON_H
 
-double get_range(double T);
-double get_dEdx(double T);
+double get_range(double T, double rho);
+double get_dEdx(double T, double rho);
 
 #endif