Time for action – comparing with assert_array_almost_equal_nulp

Let's see the assert_array_almost_equal_nulp() function in action:

  1. Determine the machine epsilon with the finfo() function:
    eps = np.finfo(float).eps
print("EPS", eps)

    The epsilon would be as follows:

    EPS 2.22044604925e-16
  2. Compare 1.0 with 1 + epsilon using the assert_almost_equal_nulp() function. Do the same for 1 + 2 * epsilon:
    print("1", np.testing.assert_array_almost_equal_nulp(1.0, 1.0 + eps))
print("2", np.testing.assert_array_almost_equal_nulp(1.0, 1.0 + 2 * eps))

    The result is as follows:

    1 None
2
Traceback (most recent call last):
  …
 assert_array_almost_equal_nulp
    raise AssertionError(msg)
AssertionError: X and Y are not equal to 1 ULP (max is 2)

What just happened?

We determined the machine epsilon with the finfo() function. We then compared 1.0 with 1 + epsilon with the assert_almost_equal_nulp() function. This test passed however, adding another epsilon resulted in an exception.

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