public static double SampleGaussian(SafeRandom random, double mean, double stddev)
{
// The method requires sampling from a uniform random of (0,1]
// but Random.NextDouble() returns a sample of [0,1).
double x1 = 1 - random.NextDouble();
double x2 = 1 - random.NextDouble();
double y1 = Math.Sqrt(-2.0 * Math.Log(x1)) * Math.Cos(2.0 * Math.PI * x2);
return(y1 * stddev + mean);
}
public static TimeSpan NextTimeSpan(this SafeRandom random, TimeSpan timeSpan)
{
if (timeSpan <= TimeSpan.Zero)
{
throw new ArgumentOutOfRangeException(nameof(timeSpan), timeSpan, "SafeRandom.NextTimeSpan timeSpan must be a positive number.");
}
double ticksD = timeSpan.Ticks * random.NextDouble();
long ticks = checked ((long)ticksD);
return(TimeSpan.FromTicks(ticks));
}
public void UpdateVelocity(Particle bestSwarmParticle, Particle globallyBestParticle)
{
for (var index = 0; index < Parameters.Count; index++)
{
var parameter = Parameters[index];
var bestParameter = BestParameters[index];
var bestSwarmParameter = bestSwarmParticle.BestParameters[index];
var globallyBestParameter = globallyBestParticle.BestParameters[index];
var velocity = _inertia * _velocities[index];
var particleMagnitude = SafeRandom.NextDouble() * _influence;
velocity += particleMagnitude * (bestParameter.Value - parameter.Value);
var swarmMagnitude = SafeRandom.NextDouble() * ParticleSwarm.Influence;
velocity += swarmMagnitude * (bestSwarmParameter.Value - parameter.Value);
var allSwarmsMagnitude = SafeRandom.NextDouble() * ParticleSwarms.Influence;
velocity += allSwarmsMagnitude * (globallyBestParameter.Value - parameter.Value);
_velocities[index] = velocity;
}
}
public void Iterate(Board Board, Search Search, Evaluation Evaluation)
{
var bestParticle = GetBestParticle();
for (var index = 0; index < Particles.Count; index++)
{
var particle = Particles[index];
if (!ReferenceEquals(particle, bestParticle) && (SafeRandom.NextDouble() <= _particleDeathPercent))
{
// Recreate particle at random location.
particle = new Particle(particle.PgnGames, particle.Parameters.DuplicateWithRandomValues());
Particles[index] = particle;
}
particle.Move();
particle.ConfigureEvaluation(Evaluation);
particle.CalculateEvaluationError(Board, Search, _winPercentScale);
}
}
public double NextDouble() => _random.NextDouble();
