2 files changed, 17 insertions, 2 deletions
diff --git a/numpy/lib/function_base.py b/numpy/lib/function_base.py
index 48b0a0830..3fb45b09a 100644
--- a/numpy/lib/function_base.py
+++ b/numpy/lib/function_base.py
@@ -3875,7 +3875,8 @@ def _quantile_is_valid(q):
 
 def _lerp(a, b, t, out=None):
     """ Linearly interpolate from a to b by a factor of t """
-    return add(a*(1 - t), b*t, out=out)
+    offset = subtract(b, a) * t
+    return add(a, offset, out=out)
 
 
 def _quantile_ureduce_func(a, q, axis=None, out=None, overwrite_input=False,
@@ -3948,6 +3949,7 @@ def _quantile_ureduce_func(a, q, axis=None, out=None, overwrite_input=False,
 
     else:
         # weight the points above and below the indices
+        #import pdb; pdb.set_trace()
 
         indices_below = not_scalar(floor(indices)).astype(intp)
         indices_above = not_scalar(indices_below + 1)
diff --git a/numpy/lib/tests/test_function_base.py b/numpy/lib/tests/test_function_base.py
index c415653e4..ea562b466 100644
--- a/numpy/lib/tests/test_function_base.py
+++ b/numpy/lib/tests/test_function_base.py
@@ -5,6 +5,10 @@ import decimal
 from fractions import Fraction
 import math
 import pytest
+import hypothesis
+from hypothesis.extra.numpy import arrays
+import hypothesis.strategies as st
+
 
 import numpy as np
 from numpy import ma
@@ -3104,7 +3108,7 @@ class TestQuantile:
         np.quantile(np.arange(100.), p, interpolation="midpoint")
         assert_array_equal(p, p0)
 
-    def test_quantile_monotic(self):
+    def test_quantile_monotonic(self):
         # GH 14685
         # test that the return value of quantile is monotonic if p0 is ordered
         p0 = np.arange(0, 1, 0.01)
@@ -3112,6 +3116,15 @@ class TestQuantile:
         equals_sorted = np.sort(quantile) == quantile
         assert equals_sorted.all()
 
+    @hypothesis.given(arr=arrays(dtype=np.float, shape=st.integers(min_value=3, max_value=1000),
+                                 elements=st.floats(allow_infinity=False, allow_nan=False)))
+    def test_quantile_monotonic_hypo(self, arr):
+        p0 = np.arange(0, 1, 0.01)
+        quantile = np.quantile(arr, p0)
+        equals_sorted = np.sort(quantile) == quantile
+        assert equals_sorted.all()
+
+
 class TestMedian:
 
     def test_basic(self):