Turn around variance and stddev

Great work, thanks!

I recommend to compute the standard deviation from variance using the sqrt, now you compute the variance as the power of a square, which might be less accurate if the value is small. This is also a little more expensive.

Changes should be little:

function standardDeviation($theSamples)
{
//[...] do this in function variance($theSamples)
// return sqrt($theSum/(count($theSamples) - 1)) ;
return sqrt($this-> variance($theSamples)) ;

}

function variance($theSamples)
{
// put stuff here from above
//return pow(Numerical::standardDeviation($theSamples), 2) ;
}

Good points. I should have thought of that and didn't. The requested change has been made and is available for download.

Thanks for the suggestion.

Dick Munroe