28.1 Definitions

A Chebyshev series is stored using the following structure,

typedef struct
{
  double * c;   /* coefficients  c[0] .. c[order] */
  int order;    /* order of expansion             */
  double a;     /* lower interval point           */
  double b;     /* upper interval point           */
  ...
} gsl_cheb_series

The approximation is made over the range [a,b] using order+1 terms, including the coefficient c[0]. The series is computed using the following convention, which is needed when accessing the coefficients directly.