/**
* It should return the standard deviation.
*/
public function testStdev()
{
$this->assertEquals(1.4142, round(Statistics::stdev(array(1, 2, 3, 4, 5)), 4));
$this->assertEquals(17.2116, round(Statistics::stdev(array(13, 23, 12, 44, 55)), 4));
$this->assertEquals(0, round(Statistics::stdev(array(1)), 4));
$this->assertEquals(0, round(Statistics::stdev(array(1, 1, 1)), 4));
$this->assertEquals(2.47, round(Statistics::stdev(array(2, 6, 4, 1, 7, 3, 6, 1, 7, 1, 6, 5, 1, 1), true), 2));
}
/**
* It should return the standard deviation.
*/
public function testStdev()
{
$this->assertEquals(1.4142, round(Statistics::stdev([1, 2, 3, 4, 5]), 4));
$this->assertEquals(17.2116, round(Statistics::stdev([13, 23, 12, 44, 55]), 4));
$this->assertEquals(0, round(Statistics::stdev([1]), 4));
$this->assertEquals(0, round(Statistics::stdev([1, 1, 1]), 4));
$this->assertEquals(2.47, round(Statistics::stdev([2, 6, 4, 1, 7, 3, 6, 1, 7, 1, 6, 5, 1, 1], true), 2));
}
/**
* Calculate and set the deviation from the mean time for each iteration. If
* the deviation is greater than the rejection threshold, then mark the iteration as
* rejected.
*/
public function computeStats()
{
$this->rejects = array();
if (0 === count($this->iterations)) {
return;
}
$times = array();
foreach ($this->iterations as $iteration) {
$times[] = $iteration->getResult()->getTime() / $iteration->getRevolutions();
}
// standard deviation for T Distribution
$this->stats['stdev'] = Statistics::stdev($times);
// mean of the times
$this->stats['mean'] = Statistics::mean($times);
// standard error
$this->stats['rstdev'] = $this->stats['stdev'] / $this->stats['mean'] * 100;
// variance
$this->stats['variance'] = Statistics::variance($times);
// min and max
$this->stats['min'] = min($times);
$this->stats['max'] = max($times);
foreach ($this->iterations as $iteration) {
// deviation is the percentage different of the value from the mean of the set.
$deviation = 100 / $this->stats['mean'] * ($iteration->getResult()->getTime() / $iteration->getRevolutions() - $this->stats['mean']);
$iteration->setDeviation($deviation);
// the Z-Value repreents the number of standard deviations this
// value is away from the mean.
$revTime = $iteration->getResult()->getTime() / $iteration->getRevolutions();
$zValue = $this->stats['stdev'] ? ($revTime - $this->stats['mean']) / $this->stats['stdev'] : 0;
$iteration->setZValue($zValue);
if (null !== $this->rejectionThreshold) {
if (abs($deviation) >= $this->rejectionThreshold) {
$this->rejects[] = $iteration;
}
}
}
$this->computed = true;
}
public function benchStDev()
{
Statistics::stdev([10, 100, 42, 84, 11, 12, 9, 6]);
}
