Energy ratio adjustments

obspy/signal/tests/test_trigger.py

@@ -4,11 +4,13 @@
 """
 import gzip
 import os
+import re
 import unittest
 import warnings
 from ctypes import ArgumentError
 
 import numpy as np
+import pytest
 from numpy.testing import assert_array_almost_equal, assert_array_equal
 
 from obspy import Stream, UTCDateTime, read
@@ -598,8 +600,8 @@ def test_classic_sta_lta_c_python(self):
 class EnergyRatioTestCase(unittest.TestCase):
 
     def test_all_zero(self):
-        a = np.zeros(100)
-        for nsta in range(len(a)):
+        a = np.zeros(10)
+        for nsta in range(1, len(a) // 2):
             with self.subTest(nsta=nsta):
                 er = energy_ratio(a, nsta=nsta)
                 assert_array_equal(er, 0)
@@ -611,15 +613,8 @@ def test_arange(self):
         er_expected = [0., 0., 0., 10., 5.5, 3.793103, 2.98, 2.519481, 0., 0.]
         assert_array_almost_equal(er, er_expected)
 
-    def test_large_nsta(self):
-        a = np.arange(100)
-        for nsta in range(len(a) // 2 + 1, len(a)):
-            with self.subTest(nsta=nsta):
-                er = energy_ratio(a, nsta=nsta)
-                assert_array_equal(er, 0)
-
     def test_all_ones(self):
-        a = np.ones(100, dtype=np.float32)
+        a = np.ones(10, dtype=np.float32)
         # Forward and backward entries are symmetric -> expecting output '1'
         # Fill nsta on both sides with zero to return same length
         for nsta in range(1, len(a) // 2 + 1):
@@ -629,12 +624,31 @@ def test_all_ones(self):
                 er_exp[nsta: len(a) - nsta + 1] = 1
                 assert_array_equal(er, er_exp)
 
+    def test_nsta_too_large(self):
+        a = np.empty(10)
+        nsta = 6
+        for nsta in (6, 10, 20):
+            expected_msg = re.escape(
+                f'nsta ({nsta}) must not be larger than half the length of '
+                f'the data (10 samples).')
+            with pytest.raises(ValueError, match=expected_msg):
+                energy_ratio(a, nsta)
+
+    def test_nsta_zero_or_less(self):
+        a = np.empty(10)
+        nsta = 6
+        for nsta in (0, -1, -10):
+            expected_msg = re.escape(
+                f'nsta ({nsta}) must not be equal to or less than zero.')
+            with pytest.raises(ValueError, match=expected_msg):
+                energy_ratio(a, nsta)
+
 
 class ModifiedEnergyRatioTestCase(unittest.TestCase):
 
     def test_all_zero(self):
-        a = np.zeros(100)
-        for nsta in range(len(a)):
+        a = np.zeros(10)
+        for nsta in range(1, len(a) // 2):
             with self.subTest(nsta=nsta):
                 er = modified_energy_ratio(a, nsta=nsta)
                 assert_array_equal(er, 0)
@@ -647,15 +661,8 @@ def test_arange(self):
                        5485.637866, 0., 0.]
         assert_array_almost_equal(er, er_expected)
 
-    def test_large_nsta(self):
-        a = np.arange(100)
-        for nsta in range(len(a) // 2 + 1, len(a)):
-            with self.subTest(nsta=nsta):
-                er = modified_energy_ratio(a, nsta=nsta)
-                assert_array_equal(er, 0)
-
     def test_all_ones(self):
-        a = np.ones(100, dtype=np.float32)
+        a = np.ones(10, dtype=np.float32)
         # Forward and backward entries are symmetric -> expecting output '1'
         # Fill nsta on both sides with zero to return same length
         for nsta in range(1, len(a) // 2 + 1):
@@ -665,6 +672,25 @@ def test_all_ones(self):
                 er_exp[nsta: len(a) - nsta + 1] = 1
                 assert_array_equal(er, er_exp)
 
+    def test_nsta_too_large(self):
+        a = np.empty(10)
+        nsta = 6
+        for nsta in (6, 10, 20):
+            expected_msg = re.escape(
+                f'nsta ({nsta}) must not be larger than half the length of '
+                f'the data (10 samples).')
+            with pytest.raises(ValueError, match=expected_msg):
+                energy_ratio(a, nsta)
+
+    def test_nsta_zero_or_less(self):
+        a = np.empty(10)
+        nsta = 6
+        for nsta in (0, -1, -10):
+            expected_msg = re.escape(
+                f'nsta ({nsta}) must not be equal to or less than zero.')
+            with pytest.raises(ValueError, match=expected_msg):
+                energy_ratio(a, nsta)
+
 
 def suite():
     return unittest.makeSuite(TriggerTestCase, 'test')

obspy/signal/trigger.py

@@ -305,10 +305,16 @@ def energy_ratio(a, nsta):
 
     .. seealso:: [Han2009]_
     """
-    if nsta > len(a) // 2 or nsta == 0:
+    if nsta > len(a) // 2:
         # Half forward, half backward -> empty medium
-        # If nsta is zero, the sum is undefined -> return zero
-        return np.zeros(len(a), dtype=np.float64)
+        msg = (
+            f'nsta ({nsta}) must not be larger than half the length of the '
+            f'data ({len(a)} samples).')
+        raise ValueError(msg)
+    if nsta <= 0:
+        # If nsta is zero, the sum is undefined
+        msg = f'nsta ({nsta}) must not be equal to or less than zero.'
+        raise ValueError(msg)
     sig_power = np.r_[0, np.cumsum(a ** 2, dtype=np.float64)]
     energy_diff = sig_power[nsta:] - sig_power[:len(sig_power) - nsta]
     er = np.zeros(len(a), dtype=np.float64)