public void Update(IVector data)
{
++Count;
using var delta = data.Subtract(Mean);
using var diff = delta.Clone();
diff.Multiply(1f / Count);
Mean.AddInPlace(diff);
using var delta2 = data.Subtract(Mean);
using var diff2 = delta.PointwiseMultiply(delta2);
M2.AddInPlace(diff2);
}