public static void UpdateVelocity(IRandom random, RealVector velocity, RealVector position, RealVector personalBest, RealVector neighborBest, double inertia = 0.721, double personalBestAttraction = 1.193, double neighborBestAttraction = 1.193, double maxVelocity = double.MaxValue)
{
var gravity = new double[velocity.Length];
var direction = new RealVector(velocity.Length);
var radius = 0.0;
var nd = new NormalDistributedRandom(random, 0, 1);
for (int i = 0; i < velocity.Length; i++)
{
var g_id = (personalBestAttraction * personalBest[i]
+ neighborBestAttraction * neighborBest[i]
- position[i] * (neighborBestAttraction + personalBestAttraction)) / 3.0;
// center of the hyper-sphere
gravity[i] = g_id + position[i];
// a random direction vector uniform over the surface of hyper-sphere, see http://mathworld.wolfram.com/HyperspherePointPicking.html
direction[i] = nd.NextDouble();
radius += g_id * g_id;
}
// randomly choose a radius within the hyper-sphere
radius = random.NextDouble() * Math.Sqrt(radius);
// unitscale is used to rescale the random direction vector to unit length, resp. length of the radius
var unitscale = Math.Sqrt(direction.DotProduct(direction));
if (unitscale > 0)
{
for (var i = 0; i < velocity.Length; i++)
{
var sampledPos = gravity[i] + direction[i] * radius / unitscale;
velocity[i] = velocity[i] * inertia + sampledPos - position[i];
}
}
var speed = Math.Sqrt(velocity.DotProduct(velocity));
if (speed > maxVelocity)
{
for (var i = 0; i < velocity.Length; i++)
{
velocity[i] *= maxVelocity / speed;
}
}
}
public static void UpdateVelocity(IRandom random, RealVector velocity, RealVector position, RealVector personalBest, RealVector neighborBest, double inertia = 0.721, double personalBestAttraction = 1.193, double neighborBestAttraction = 1.193, double maxVelocity = double.MaxValue)
{
for (int i = 0; i < velocity.Length; i++)
{
double r_p = random.NextDouble();
double r_g = random.NextDouble();
velocity[i] =
velocity[i] * inertia +
(personalBest[i] - position[i]) * personalBestAttraction * r_p +
(neighborBest[i] - position[i]) * neighborBestAttraction * r_g;
}
var speed = Math.Sqrt(velocity.DotProduct(velocity));
if (speed > maxVelocity)
{
for (var i = 0; i < velocity.Length; i++)
{
velocity[i] *= maxVelocity / speed;
}
}
}
