move the phi_modulo into the if condition for optimisation

Author: burmist-git

src/ctapipe/image/muon/intensity_fitter.py

@@ -80,9 +80,7 @@ def chord_length(radius, rho, phi, phi0=0):
 def _chord_length(radius, rho, phi, phi0):
     phi = phi - phi0
 
-    phi_modulo = (phi + np.pi) % (2 * np.pi) - np.pi
-
-    discriminant_norm = 1 - (rho**2 * np.sin(phi_modulo) ** 2)
+    discriminant_norm = 1 - (rho**2 * np.sin(phi) ** 2)
     if discriminant_norm < 0:
         return 0
 
@@ -91,7 +89,7 @@ def _chord_length(radius, rho, phi, phi0):
     if rho <= 1.0:
         # muon has hit the mirror
         effective_chord_length = radius * (
-            np.sqrt(discriminant_norm) + rho * np.cos(phi_modulo)
+            np.sqrt(discriminant_norm) + rho * np.cos(phi)
         )
 
         return effective_chord_length
@@ -100,6 +98,7 @@ def _chord_length(radius, rho, phi, phi0):
         # muon did not hit the mirror
         effective_chord_length = 2 * radius * np.sqrt(discriminant_norm)
         # Filtering out non-physical solutions for phi
+        phi_modulo = (phi + np.pi) % (2 * np.pi) - np.pi
         if np.abs(phi_modulo) > np.arcsin(1.0 / rho):
             return 0