feat(core.py): add ackley

src/fbench/core.py

@@ -1,6 +1,51 @@
 import numpy as np
 
 
+def ackley(x):
+    """Ackley function.
+
+    .. math::
+
+        f(\\mathbf{x}) =
+        -20 \\exp \\left(
+            -0.2 \\sqrt{ \\frac{1}{n} \\sum_{i=1}^n x_i^2 }
+        \\right)
+        - \\exp \\left( \\frac{1}{n} \\sum_{i=1}^n \\cos(2 \\pi x_i) \\right)
+        + 20
+        + e
+
+    Parameters
+    ----------
+    x : array_like
+        A real-valued vector to evaluate.
+
+    Returns
+    -------
+    float
+        Function value at x.
+
+    References
+    ----------
+    .. [1] "Test functions for optimization", Wikipedia,
+           `<https://en.wikipedia.org/wiki/Test_functions_for_optimization>`_
+
+    Examples
+    --------
+    >>> round(ackley([0, 0]), 4)
+    0.0
+
+    >>> round(ackley([1, 1]), 4)
+    3.6254
+    """
+    x = np.asarray(x)
+    return float(
+        -20 * np.exp(-0.2 * np.sqrt((x**2).mean()))
+        - np.exp((np.cos(2 * np.pi * x)).sum() / len(x))
+        + 20
+        + np.e
+    )
+
+
 def sphere(x):
     """Sphere function.
 

tests/test_core.py

@@ -3,6 +3,20 @@
 from fbench import core
 
 
+@pytest.mark.parametrize(
+    "arg, expected",
+    [
+        ([0], 0.0),
+        ([0, 0], 0.0),
+        ([1, 1], 3.6254),
+        ([2, 2], 6.5936),
+    ],
+)
+def test_ackley(arg, expected):
+    actual = core.ackley(x=arg)
+    assert round(actual, 4) == expected
+
+
 @pytest.mark.parametrize(
     "arg, expected",
     [