/**
* Sigmoid is just a special case of the logistic function.
*/
public function testSigmoid()
{
$this->assertEquals(Special::logistic(1, 1, 1, 2), Special::sigmoid(1));
$this->assertEquals(Special::logistic(1, 1, 2, 2), Special::sigmoid(2));
$this->assertEquals(Special::logistic(1, 1, 3, 2), Special::sigmoid(3));
$this->assertEquals(Special::logistic(1, 1, 4, 2), Special::sigmoid(4));
$this->assertEquals(Special::logistic(1, 1, 4.6, 2), Special::sigmoid(4.6));
}