// Wild Magic Source Code
// David Eberly
// http://www.geometrictools.com
// Copyright (c) 1998-2007
//
// This library is free software; you can redistribute it and/or modify it
// under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation; either version 2.1 of the License, or (at
// your option) any later version.  The license is available for reading at
// either of the locations:
//     http://www.gnu.org/copyleft/lgpl.html
//     http://www.geometrictools.com/License/WildMagicLicense.pdf
//
// Version: 4.0.0 (2006/06/28)

#ifndef WM4APPRPOLYFIT4_H
#define WM4APPRPOLYFIT4_H

#include "Wm4FoundationLIB.h"
#include "Wm4System.h"

namespace Wm4
{

// The samples are (x[i],y[i],z[i],w[i]) for 0 <= i < S.  Think of w as a
// function of x, y, and z, say w = f(x,y,z).  The function fits the samples
// with a polynomial of degree d0 in x, degree d1 in y, and degree d2 in z,
// say
//   w = sum_{i=0}^{d0} sum_{j=0}^{d1} sum_{k=0}^{d2} c[i][j][k]*x^i*y^j*z^k
// The method is a least-squares fitting algorithm.  The return array stores
// the c[i][j][k] values according to
//   returned[i+(d0+1)*(j+(d1+1)*k)] = c[i][j][k]
// for a total of (d0+1)*(d1+1)*(d2+1) coefficients.  The caller is
// responsible for deleting the input arrays if they were dynamically
// allocated.  The caller is also responsible for deleting the returned array.
//
// WARNING.  The fitting algorithm for polynomial terms
//   (1,x,x^2,...,x^d0), (1,y,y^2,...,y^d1), (1,z,z^2,...,z^d2)
// is known to be nonrobust for large degrees and for large magnitude data.
// One alternative is to use orthogonal polynomials
//   (f[0](x),...,f[d0](x)), (g[0](y),...,g[d1](y)), (h[0](z),...,h[d2](z))
// and apply the least-squares algorithm to these.  Another alternative is to
// transform
//   (x',y',z',w') = ((x-xcen)/rng, (y-ycen)/rng, (z-zcen)/rng, w/rng)
// where xmin = min(x[i]), xmax = max(x[i]), xcen = (xmin+xmax)/2,
// ymin = min(y[i]), ymax = max(y[i]), ycen = (ymin+ymax)/2, zmin = min(z[i]),
// zmax = max(z[i]), zcen = (zmin+zmax)/2, and
// rng = max(xmax-xmin,ymax-ymin,zmax-zmin).  Fit the (x',y',z',w') points,
//   w' = sum_{i=0}^{d0} sum_{j=0}^{d1} sum_{k=0}^{d2} c'[i][j][k] *
//          (x')^i*(y')^j*(z')^k
// The original polynomial is evaluated as
//   w = rng * sum_{i=0}^{d0} sum_{j=0}^{d1} sum_{k=0}^{d2} c'[i][j][k] *
//         ((x-xcen)/rng)^i * ((y-ycen)/rng)^j * ((z-zcen)/rng)^k

template <class Real> WM4_FOUNDATION_ITEM
Real* PolyFit4 (int iSamples, const Real* afX, const Real* afY,
    const Real* afZ, const Real* afW, int iXDegree, int iYDegree,
    int iZDegree);

}

#endif
