/**
* Compute chiSquare test value from array of observations
* and expected probabilities of slots.
*
* @param array(int) $observedCnt observed counts
* @param array(double) $expectedProb expected probabilities
*
* @returns double chi squared
*/
static function chiSquare(array $observedCnt, array $expectedProb)
{
Preconditions::check(count($observedCnt) == count($expectedProb), "number of slots for observations and expectations should match.");
foreach ($observedCnt as $cnt) {
Preconditions::check(is_int($cnt), "Observed count should be integer");
}
foreach ($expectedProb as $prob) {
Preconditions::check(is_double($prob), "Probability should be double");
Preconditions::check(0.0 < $prob && 1.0 > $prob, "Expected probabilities shoud be in range (0,1).");
}
Preconditions::check(abs(array_sum($expectedProb) - 1) < 1.0E-6, "Probabilities does not sum up to 1");
$samples = array_sum($observedCnt);
foreach ($expectedProb as $prob) {
if ($samples * $prob <= 5) {
// @see http://en.wikipedia.org/wiki/Pearson's_chi-square_test#Problems
throw new RuntimeException("You should have more samples for " . "computing Pearson test with specified probabilities");
}
}
$chisqr = 0;
for ($i = 0; $i < count($observedCnt); $i++) {
$expected = $expectedProb[$i] * $samples;
$chisqr += Math::sqr($observedCnt[$i] - $expected) / $expected;
}
return $chisqr;
}
public function testSqr()
{
$this->assertSame(0, Math::sqr(0));
$this->assertSame(1, Math::sqr(-1));
$this->assertSame(1, Math::sqr(1));
$this->assertSame(4, Math::sqr(2));
$this->assertSame(4.0, Math::sqr(2.0));
$this->assertEquals(1.7689, Math::sqr(1.33), '', 1.0E-10);
}
