From b61c2fbc09dfed35bf5905d23a894895d043127d Mon Sep 17 00:00:00 2001
From: Alison Mitchell <amwmitchell@gmail.com>
Date: Tue, 23 Mar 2021 15:38:47 +0100
Subject: [PATCH] add validation function for psf norm

---
 pyirf/validation.py | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)
 create mode 100644 pyirf/validation.py

diff --git a/pyirf/validation.py b/pyirf/validation.py
new file mode 100644
index 000000000..1ffc7c248
--- /dev/null
+++ b/pyirf/validation.py
@@ -0,0 +1,18 @@
+import numpy as np
+from .utils import cone_solid_angle
+
+class InvalidIRF(Exception):
+    pass
+
+class InvalidNormalisation(InvalidIRF):
+    pass
+
+def validate_psf(psf,source_offset_bins):
+    
+    radbin_solidangle = np.diff(cone_solid_angle(source_offset_bins))
+    integral = np.sum(psf*radbin_solidangle,axis=2)
+    
+    if not np.allclose(integral,1):
+        nbad = np.count_nonzero(~np.isclose(integral,1))
+        raise InvalidNormalisation(f"PSF not correctly normalised: {nbad} affected bins")
+    
\ No newline at end of file