/**
* 割り算の検証。10/5=2となることを検証する
*/
public function testDivision()
{
$this->assertEquals(2, $this->arithmetic->division(10, 5));
}
/**
* When a polynomial is being evaluated at a point x₀, build a callback
* function and return the value of the callback function at x₀
* Example: $polynomial = new Polynomial([1, -8, 12, 3]);
* echo $polynomial(4);
* // prints -13
*
* @param number $x₀ The value at which we are evaluting our polynomial
*
* @return number The result of our polynomial evaluated at $x₀
*/
public function __invoke($x₀) : float
{
// Set object parameters as local variables so they can be used with the use function
$degree = $this->degree;
$coefficients = $this->coefficients;
// Start with the zero polynomial
$polynomial = function ($x) {
return 0;
};
// Iterate over each coefficient to create a callback function for each term
for ($i = 0; $i < $degree + 1; $i++) {
// Create a callback function for the current term
$term = function ($x) use($degree, $coefficients, $i) {
return $coefficients[$i] * $x ** ($degree - $i);
};
// Add the new term to the polynomial
$polynomial = Arithmetic::add($polynomial, $term);
}
return $polynomial($x₀);
}
public function testNestedArithmetic()
{
// f(x) = x - 9
$f = function ($x) {
return $x - 9;
};
// g(x) = x + 2
$g = function ($x) {
return $x + 2;
};
// h(x) = x
$h = function ($x) {
return $x;
};
// Π(x) = $f(x) * ( g(x) + h(x) ) = (x - 9) * (2x + 2) = 2x² - 16x - 18
$product = Arithmetic::multiply($f, Arithmetic::add($g, $h));
// Π(0) = -18
$expected = -18;
$x = $product(0);
$this->assertEquals($expected, $x);
// Π(5) = -48
$expected = -48;
$x = $product(5);
$this->assertEquals($expected, $x);
// Π(-5) = 112
$expected = 112;
$x = $product(-5);
$this->assertEquals($expected, $x);
}
