static public void Initialize(BodyInitializer initializer, float clusterScale,
float velocityScale, int numBodies,
out float4[] positions, out float4[] velocities)
{
var pscale = clusterScale*Math.Max(1.0f, numBodies/1024.0f);
var vscale = velocityScale*pscale;
initializer.NumBodies = numBodies;
initializer.PScale = pscale;
initializer.VScale = vscale;
positions = Enumerable.Range(0, numBodies).Select(initializer.Position).ToArray();
velocities = positions.Select(initializer.Velocity).ToArray();
// now we try to adjust velocity to make total momentum = zero.
var momentums = velocities.Select(Momentum).ToArray();
var totalMomentum = momentums.Aggregate(new float4(0.0f, 0.0f, 0.0f, 0.0f),
(accum, momentum) =>
new float4(accum.x + momentum.x,
accum.y + momentum.y,
accum.z + momentum.z,
accum.w + momentum.w));
Console.WriteLine("total momentum and mass 0 = {0}", totalMomentum);
var len = velocities.Length;
// adjust velocities
velocities = velocities.Select((vel, i) => new float4(
vel.x - totalMomentum.x / len / vel.w,
vel.y - totalMomentum.y / len / vel.w,
vel.z - totalMomentum.z / len / vel.w,
vel.w)).ToArray();
// see total momentum after adjustment
momentums = velocities.Select(Momentum).ToArray();
totalMomentum = momentums.Aggregate(new float4(0.0f, 0.0f, 0.0f, 0.0f),
(accum, momentum) =>
new float4(accum.x + momentum.x,
accum.y + momentum.y,
accum.z + momentum.z,
accum.w + momentum.w));
Console.WriteLine("total momentum and mass 1 = {0}", totalMomentum);
}
