ENH: add assert_array_max_ulp comparison function.

This new comparison raises an error if the number of representable
numbers between two arrays exceeds a tolerance.

1 files changed, 12 insertions, 1 deletions

diff --git a/numpy/testing/utils.py b/numpy/testing/utils.py
index 3e789272e..c5be4c49d 100644
--- a/numpy/testing/utils.py
+++ b/numpy/testing/utils.py
@@ -14,7 +14,8 @@ __all__ = ['assert_equal', 'assert_almost_equal','assert_approx_equal',
            'assert_array_almost_equal', 'assert_raises', 'build_err_msg',
            'decorate_methods', 'jiffies', 'memusage', 'print_assert_equal',
            'raises', 'rand', 'rundocs', 'runstring', 'verbose', 'measure',
-           'assert_', 'spacing', 'assert_array_almost_equal_nulp']
+           'assert_', 'spacing', 'assert_array_almost_equal_nulp',
+           'assert_array_max_ulp']
 
 verbose = 0
 
@@ -1110,6 +1111,16 @@ def assert_array_almost_equal_nulp(x, y, nulp=1):
         raise AssertionError("X and Y are not equal to %d ULP "\
                              "(max is %d)" % (nulp, max_nulp))
 
+def assert_array_max_ulp(a, b, maxulp=1, dtype=None):
+    """Given two arrays a and b, check that every item differs in at most N
+    Unit in the Last Place."""
+    import numpy as np
+    ret = nulp_diff(a, b, dtype)
+    if not np.all(ret <= maxulp):
+        raise AssertionError("Arrays are not almost equal up to %d ULP" % \
+                             maxulp)
+    return ret
+
 def nulp_diff(x, y, dtype=None):
     """For each item in x and y, eeturn the number of representable floating
     points between them.