/// <summary>
/// Generates the coordinates of a point within an ellipsoid.
/// https://blogs.sas.com/content/iml/2016/04/06/generate-points-uniformly-in-ball.html
/// </summary>
/// <param name="gauss"> Std Normal Dist for generating samples; </param>
/// <param name="conditionalR"> Maximum ellipsoid radius across certain axis; </param>
private static float[] SampleWithinEllipsoid(
NormalDistribution gauss,
double[] conditionalR,
int featureDim,
float[,] clustersCentroids,
int clusterIndex)
{
var y = gauss.GenerateSample(featureDim);
var yl2 = y.L2Norm();
var u = Random.NextDouble();
var udr = new double[conditionalR.Length];
for (var i = 0; i < udr.Length; i++)
{
udr[i] = Math.Pow(u, 1.0 / y.Length) * conditionalR[i];
}
for (var i = 0; i < y.Length; i++)
{
var c = clustersCentroids[clusterIndex, i];
y[i] = c + (float)(udr[i] * (y[i] / yl2));
}
return(y);
}
/// <summary>
/// Generates the coordinates of a point within a sphere.
/// https://blogs.sas.com/content/iml/2016/04/06/generate-points-uniformly-in-ball.html
/// </summary>
/// <param name="gauss"> Std Normal Dist for generating samples; </param>
/// <param name="r"> Sphere Radius; </param>
private static float[] SampleWithinSphere(
NormalDistribution gauss,
double r,
int featureDim,
float[,] clustersCentroids,
int clusterIndex)
{
var y = gauss.GenerateSample(featureDim);
var yl2 = y.L2Norm();
var u = Random.NextDouble();
var udr = Math.Pow(u, 1.0 / y.Length) * r;
for (var i = 0; i < y.Length; i++)
{
var c = clustersCentroids[clusterIndex, i];
y[i] = (float)(udr * (y[i] / yl2));
}
return(y);
}
