BUG: fix interpolation with inf and NaN present

Values like NaN and inf would result in wrong interpolated values on
exactly matching sampling points. To produce the correct behavior, we
add an additional check to avoid interpolation when handling such a
point.

Closes #11439

1 files changed, 14 insertions, 0 deletions

diff --git a/numpy/lib/tests/test_function_base.py b/numpy/lib/tests/test_function_base.py
index 4103a9eb3..d2a9181db 100644
--- a/numpy/lib/tests/test_function_base.py
+++ b/numpy/lib/tests/test_function_base.py
@@ -2237,6 +2237,14 @@ class TestInterp(object):
         x0 = np.nan
         assert_almost_equal(np.interp(x0, x, y), x0)
 
+    def test_non_finite_behavior(self):
+        x = [1, 2, 2.5, 3, 4]
+        xp = [1, 2, 3, 4]
+        fp = [1, 2, np.inf, 4]
+        assert_almost_equal(np.interp(x, xp, fp), [1, 2, np.inf, np.inf, 4])
+        fp = [1, 2, np.nan, 4]
+        assert_almost_equal(np.interp(x, xp, fp), [1, 2, np.nan, np.nan, 4])
+
     def test_complex_interp(self):
         # test complex interpolation
         x = np.linspace(0, 1, 5)
@@ -2251,6 +2259,12 @@ class TestInterp(object):
         x0 = 2.0
         right = 2 + 3.0j
         assert_almost_equal(np.interp(x0, x, y, right=right), right)
+        # test complex non finite
+        x = [1, 2, 2.5, 3, 4]
+        xp = [1, 2, 3, 4]
+        fp = [1, 2+1j, np.inf, 4]
+        y = [1, 2+1j, np.inf+0.5j, np.inf, 4]
+        assert_almost_equal(np.interp(x, xp, fp), y)
         # test complex periodic
         x = [-180, -170, -185, 185, -10, -5, 0, 365]
         xp = [190, -190, 350, -350]