def test_sigmoid():
    def ref_sigmoid(x):
        if x >= 0:
            return 1 / (1 + np.exp(-x))
        else:
            z = np.exp(x)
            return z / (1 + z)
    sigmoid = np.vectorize(ref_sigmoid)

    x = K.placeholder(ndim=2)
    f = K.function([x],  [activations.sigmoid(x)])
    test_values = get_standard_values()

    result = f([test_values])[0]
    expected = sigmoid(test_values)
    assert_allclose(result, expected, rtol=1e-05)
Test using a numerically stable reference sigmoid implementation
dataset/ETHPy150Open fchollet/keras/tests/keras/test_activations.py/test_sigmoid