internal void ComputeForces()
{
foreach (var u in particles[0])
{
foreach (var v in particles[0])
{
if (u != v)
{
u.force += MultipoleCoefficients.Force(u.point, v.point);
}
}
}
}
/// <summary>
/// Compute forces between particles using multipole approximations.
/// </summary>
/// <param name="precision"></param>
public void ComputeForces(int precision)
{
root.computeMultipoleCoefficients(precision);
foreach (var l in leaves)
{
l.ComputeForces();
List <KdNode> stack = new List <KdNode>();
stack.Add(root);
while (stack.Count > 0)
{
KdNode v = stack.Last();
stack.RemoveAt(stack.Count - 1);
if (!l.intersects(v))
{
foreach (var p in l.particles[0])
{
p.force -= v.multipoleCoefficients.ApproximateForce(p.point);
}
}
else
{
var leaf = v as LeafKdNode;
if (leaf != null)
{
foreach (var p in l.particles[0])
{
foreach (var q in leaf.particles[0])
{
if (p != q)
{
p.force += MultipoleCoefficients.Force(p.point, q.point);
}
}
}
}
else
{
var n = v as InternalKdNode;
stack.Add(n.leftChild);
stack.Add(n.rightChild);
}
}
}
}
}
void ComputeRepulsiveForces(FiNode[] vs)
{
int n = vs.Length;
if (n > 16 && settings.ApproximateRepulsion)
{
var ps = new KDTree.Particle[vs.Length];
// before calculating forces we perturb each center by a small vector in a unique
// but deterministic direction (by walking around a circle in n steps) - this allows
// the KD-tree to decompose even when some nodes are at exactly the same position
double angle = 0, angleDelta = 2.0 * Math.PI / n;
for (int i = 0; i < n; ++i)
{
ps[i] = new KDTree.Particle(vs[i].Center + 1e-5 * new Point(Math.Cos(angle), Math.Sin(angle)));
angle += angleDelta;
}
var kdTree = new KDTree(ps, 8);
kdTree.ComputeForces(5);
for (int i = 0; i < vs.Length; ++i)
{
AddRepulsiveForce(vs[i], ps[i].force);
}
}
else
{
foreach (FiNode u in vs)
{
var fu = new Point();
foreach (FiNode v in vs)
{
if (u != v)
{
fu += MultipoleCoefficients.Force(u.Center, v.Center);
}
}
AddRepulsiveForce(u, fu);
}
}
}