Fix incorrect integrals in PieceWiseLinFunc (#38)

Integrals of piece-wise linear functions were incorrect if the
requested interval lies completely between two support points.
This has been fixed, and a unit test exercising this behavior
was added.

Fixes #38

2 files changed, 42 insertions, 14 deletions

diff --git a/pyspike/PieceWiseLinFunc.py b/pyspike/PieceWiseLinFunc.py
index 8145e63..8faaec4 100644
--- a/pyspike/PieceWiseLinFunc.py
+++ b/pyspike/PieceWiseLinFunc.py
@@ -146,31 +146,47 @@ class PieceWiseLinFunc:
 
         if interval is None:
             # no interval given, integrate over the whole spike train
-            integral = np.sum((self.x[1:]-self.x[:-1]) * 0.5*(self.y1+self.y2))
+            return np.sum((self.x[1:]-self.x[:-1]) * 0.5*(self.y1+self.y2))
+
+        # find the indices corresponding to the interval
+        start_ind = np.searchsorted(self.x, interval[0], side='right')
+        end_ind = np.searchsorted(self.x, interval[1], side='left')-1
+        assert start_ind > 0 and end_ind < len(self.x), \
+            "Invalid averaging interval"
+        if start_ind > end_ind:
+            print(start_ind, end_ind, self.x[start_ind])
+            # contribution from between two closest edges
+            y_x0 = intermediate_value(self.x[start_ind-1],
+                                        self.x[start_ind],
+                                        self.y1[start_ind-1],
+                                        self.y2[start_ind-1],
+                                        interval[0])
+            y_x1 = intermediate_value(self.x[start_ind-1],
+                                        self.x[start_ind],
+                                        self.y1[start_ind-1],
+                                        self.y2[start_ind-1],
+                                        interval[1])
+            print(y_x0, y_x1, interval[1] - interval[0])
+            integral = (y_x0 + y_x1) * 0.5 * (interval[1] - interval[0])
+            print(integral)
         else:
-            # find the indices corresponding to the interval
-            start_ind = np.searchsorted(self.x, interval[0], side='right')
-            end_ind = np.searchsorted(self.x, interval[1], side='left')-1
-            assert start_ind > 0 and end_ind < len(self.x), \
-                "Invalid averaging interval"
             # first the contribution from between the indices
             integral = np.sum((self.x[start_ind+1:end_ind+1] -
-                               self.x[start_ind:end_ind]) *
-                              0.5*(self.y1[start_ind:end_ind] +
-                                   self.y2[start_ind:end_ind]))
+                            self.x[start_ind:end_ind]) *
+                            0.5*(self.y1[start_ind:end_ind] +
+                                self.y2[start_ind:end_ind]))
             # correction from start to first index
             integral += (self.x[start_ind]-interval[0]) * 0.5 * \
                         (self.y2[start_ind-1] +
-                         intermediate_value(self.x[start_ind-1],
+                        intermediate_value(self.x[start_ind-1],
                                             self.x[start_ind],
                                             self.y1[start_ind-1],
                                             self.y2[start_ind-1],
-                                            interval[0]
-                                            ))
+                                            interval[0]))
             # correction from last index to end
             integral += (interval[1]-self.x[end_ind]) * 0.5 * \
                         (self.y1[end_ind] +
-                         intermediate_value(self.x[end_ind], self.x[end_ind+1],
+                        intermediate_value(self.x[end_ind], self.x[end_ind+1],
                                             self.y1[end_ind], self.y2[end_ind],
                                             interval[1]
                                             ))
diff --git a/test/test_function.py b/test/test_function.py
index ddeb4b1..6c04839 100644
--- a/test/test_function.py
+++ b/test/test_function.py
@@ -136,7 +136,7 @@ def test_pwc_integral():
     # test part interval, spanning an edge
     assert_equal(f1.integral((0.5,1.5)), 0.5*1.0 + 0.5*-0.5)
     # test part interval, just over two edges
-    assert_almost_equal(f1.integral((1.0-1e-16,2+1e-16)), 1.0*-0.5, decimal=16)
+    assert_almost_equal(f1.integral((1.0-1e-16,2+1e-16)), 1.0*-0.5, decimal=14)
     # test part interval, between two edges
     assert_equal(f1.integral((1.0,2.0)), 1.0*-0.5)
     assert_equal(f1.integral((1.2,1.7)), (1.7-1.2)*-0.5)
@@ -212,6 +212,18 @@ def test_pwl():
     a = f.avrg([1.0, 4.0])
     assert_almost_equal(a, (-0.45 + 0.75 + 1.5*0.5) / 3.0, decimal=16)
 
+    # interval between support points
+    a = f.avrg([1.1, 1.5])
+    assert_almost_equal(a, (-0.5+0.1*0.1 - 0.45) * 0.5, decimal=14)
+
+    # starting at a support point
+    a = f.avrg([1.0, 1.5])
+    assert_almost_equal(a, (-0.5 - 0.45) * 0.5, decimal=14)
+
+    # start and end at support point
+    a = f.avrg([1.0, 2.0])
+    assert_almost_equal(a, (-0.5 - 0.4) * 0.5, decimal=14)
+    
     # averaging over multiple intervals
     a = f.avrg([(0.5, 1.5), (1.5, 2.5)])
     assert_almost_equal(a, (1.375*0.5 - 0.45 + 0.75)/2.0, decimal=16)