public static RationalFunction ConvertToRationalFunction(this alglib.barycentricinterpolant function)
{
if (function == null)
{
throw new ArgumentNullException();
}
var n = function.innerobj.n;
if (n <= 2)
{
// linear function, let's convert it to that form for simplicity
double[] coefficients;
alglib.polynomialbar2pow(function, out coefficients);
return(RationalFunction.BuildPolynomial(coefficients.Select(x => (float)x).ToArray()));
}
else
{
// maintain barycentric representation
var w = ConvertToFloatArray(function.innerobj.w, n);
var x = ConvertToFloatArray(function.innerobj.x, n);
var y = ConvertToFloatArray(function.innerobj.y, n);
return(RationalFunction.BuildBarycentric(w, x, y, (float)function.innerobj.sy));
}
}
public static RationalFunction BuildPolynomial(params float[] coefficients)
{
if (coefficients == null)
{
throw new ArgumentNullException();
}
if (coefficients.Length > MaxOrder)
{
throw new ArgumentException("Maximum supported order exceeded.");
}
var result = new RationalFunction();
result.FunctionForm = RationalFunctionForm.PolynomialForm;
result.Order = (ushort)coefficients.Length;
result.W = new float[MaxOrder];
coefficients.CopyTo(result.W, 0);
result.SY = 1.0f;
return(result);
}
public static RationalFunction BuildBarycentric(float[] w, float[] x, float[] y, float sy)
{
if (w == null || x == null || y == null)
{
throw new ArgumentNullException();
}
if (w.Length != x.Length || x.Length != y.Length)
{
throw new ArgumentException("Mismatched array lengths.");
}
if (!IsSorted(x))
{
throw new ArgumentException("Points are not sorted by x coordinate.");
}
if (!w.All(wi => Math.Abs(wi) <= 1))
{
throw new ArgumentException("Weight values are not normalized to -1 to 1 range.");
}
if (!y.All(yi => Math.Abs(yi) <= 1))
{
throw new ArgumentException("Y values are not normalized to -1 to 1 range.");
}
var result = new RationalFunction();
result.FunctionForm = RationalFunctionForm.BarycentricForm;
result.Order = (ushort)w.Length;
result.W = new float[MaxOrder];
w.CopyTo(result.W, 0);
result.X = new float[MaxOrder];
x.CopyTo(result.X, 0);
result.Y = new float[MaxOrder];
y.CopyTo(result.Y, 0);
result.SY = sy;
return(result);
}
