CalcPolyFit

The method CalcPolyFit calculates the best fit for a polynomial of order nOrder. The order of the polynomial is restricted to values between 1 and MaxPolyFitOrder. Higher orders will result in numerical instabilities. The variable array parameter kArray returns the polynomial coefficients, the variable parameter FitQual returns the goodness of fit. The function CalcPolyFit returns a TRUE value if the fit has been calculated successfully, and the returned parameters are valid.

Hint 1:

The number of data used for the polynomial fit has to exceed the order of the polynomial at least by one.

Hint 2:

The declaration of CalcPolyFit in C++ slightly differs from the Pascal declaration (note the extra parameter kArray_Size): bool __fastcall CalcPolyFit(const Byte nOrder, double * kArray, const int kArray_Size, double &FitQual);

Hint 3:

The algorithm for calculating the polynomial fit has been changed with release 9.0 of the SDL Component Suite. This change results in radical improvement of results for ill-conditioned problems (i.e. when x values are not centered around zero). Thus you should always use release 9.0, or higher, for high order polynomials.

Example:

This method is used in the following example program (see http://www.lohninger.com/examples.html for downloading the code): curvefit