BUG: Fixed maximum relative error reporting in assert_allclose (numpy…

…gh-13802)

Fixed maximum relative error reporting in assert_allclose:

In cases where the two arrays have zeros at the same positions it will
no longer report nan as the max relative error

numpy/testing/_private/utils.py

@@ -686,7 +686,7 @@ def assert_array_compare(comparison, x, y, err_msg='', verbose=True,
                          header='', precision=6, equal_nan=True,
                          equal_inf=True):
     __tracebackhide__ = True  # Hide traceback for py.test
-    from numpy.core import array, array2string, isnan, inf, bool_, errstate
+    from numpy.core import array, array2string, isnan, inf, bool_, errstate, all
 
     x = array(x, copy=False, subok=True)
     y = array(y, copy=False, subok=True)
@@ -807,7 +807,12 @@ def func_assert_same_pos(x, y, func=isnan, hasval='nan'):
 
                     # note: this definition of relative error matches that one
                     # used by assert_allclose (found in np.isclose)
-                    max_rel_error = (error / abs(y)).max()
+                    # Filter values where the divisor would be zero
+                    nonzero = bool_(y != 0)
+                    if all(~nonzero):
+                        max_rel_error = array(inf)
+                    else:
+                        max_rel_error = (error[nonzero] / abs(y[nonzero])).max()
                     if error.dtype == 'object':
                         remarks.append('Max relative difference: '
                                         + str(max_rel_error))

numpy/testing/tests/test_utils.py

@@ -881,6 +881,15 @@ def test_equal_nan_default(self):
         assert_array_less(a, b)
         assert_allclose(a, b)
 
+    def test_report_max_relative_error(self):
+        a = np.array([0, 1])
+        b = np.array([0, 2])
+
+        with pytest.raises(AssertionError) as exc_info:
+            assert_allclose(a, b)
+        msg = str(exc_info.value)
+        assert_('Max relative difference: 0.5' in msg)
+
 
 class TestArrayAlmostEqualNulp(object):