/*
* Random variates from the hypergeometric distribution.
*
* Returns the number of white balls drawn when kk balls
* are drawn at random from an urn containing nn1 white
* and nn2 black balls.
*/
private static double RHyper(long kk, double nn1, double nn2, CoinFlipper coins)
{
var prng = new PRNG(coins);
if (kk > 10)
{
return(HypergeometricHRUA(prng, nn1, nn2, kk));
}
else
{
return(HypergeometricHYP(prng, nn1, nn2, kk));
}
}
internal static long SampleUniform(ValueRange valueRange, CoinFlipper coins)
{
var currentRange = valueRange.Copy();
if (currentRange.Size() == 0)
{
throw new Exception("");
}
while (currentRange.Size() > 1)
{
var mid = (currentRange.Start + currentRange.End) / 2;
var bit = coins.GetCoin();
if (bit)
{
currentRange.Start = mid + 1;
}
else
{
currentRange.End = mid;
}
}
return(currentRange.Start);
}
public PRNG(CoinFlipper coins)
{
_coins = coins;
}
/*
* Get a sample from the hypergeometric distribution, using the provided bit list as a source of randomness
*/
internal static long SampleHGD(ValueRange inRange, ValueRange outRange, long mid, CoinFlipper coins)
{
var inSize = inRange.Size();
var outSize = outRange.Size();
if (inSize < 0 || outSize < 0 || inSize > outSize || !outRange.Contains(mid))
{
throw new ArgumentException();
}
var nSampleIndex = mid - outRange.Start + 1;
if (inSize == outSize)
{
return(inRange.Start + nSampleIndex - 1);
}
double inSampleNum = RHyper(nSampleIndex, inSize, outSize - inSize, coins);
if (inSampleNum == 0)
{
return(inRange.Start);
}
else
{
var inSample = inRange.Start + inSampleNum - 1;
if (!inRange.Contains(Convert.ToInt32(inSample)))
{
throw new ArgumentException();
}
return(Convert.ToInt32(inSample));
}
}
