use symmetric lerp function

2 files changed, 5 insertions, 9 deletions

diff --git a/numpy/lib/function_base.py b/numpy/lib/function_base.py
index 6799b2a4f..f56a8844e 100644
--- a/numpy/lib/function_base.py
+++ b/numpy/lib/function_base.py
@@ -3875,14 +3875,10 @@ def _quantile_is_valid(q):
 
 def _lerp(a, b, t, out=None):
     """ Linearly interpolate from a to b by a factor of t """
-    #a + (b-a)*t if t < 0.5 else b - (b-a)*(1-t)
-    #if t < 0.5:
-    #    return add(a, subtract(b, a)*t, out=out)
-    #else:
-    #    return subtract(b, subtract(b, a)*(1-t), out=out)
-    # a + (b-a)*t
-    offset = subtract(b, a) * t
-    return add(a, offset, out=out)
+    if t < 0.5:
+        return add(a, subtract(b, a)*t, out=out)
+    else:
+        return subtract(b, subtract(b, a)*(1-t), out=out)
 
 
 def _quantile_ureduce_func(a, q, axis=None, out=None, overwrite_input=False,
diff --git a/numpy/lib/tests/test_function_base.py b/numpy/lib/tests/test_function_base.py
index de2716bf1..8ef72ea21 100644
--- a/numpy/lib/tests/test_function_base.py
+++ b/numpy/lib/tests/test_function_base.py
@@ -3153,7 +3153,7 @@ class TestLerp:
                       a=st.floats(allow_nan=False, allow_infinity=False),
                       b=st.floats(allow_nan=False, allow_infinity=False))
     def test_lerp_symmetric(self, t, a, b):
-        assert np.isclose(np.lib.function_base._lerp(a, b, t), np.lib.function_base._lerp(b, a, (1-t)))
+        assert np.lib.function_base._lerp(a, b, 1 - (1 - t)) == np.lib.function_base._lerp(b, a, 1 - t)
 
 
 class TestMedian: