Chebyshev.cpp

#include "Headers.h"
#include "Chebyshev.h"

int ChebEval(const ChebSeries* cs, const double x, MathResult* result)
{
    int j;
    double d  = 0.0;
    double dd = 0.0;

    double y  = (2.0*x - cs->a - cs->b) / (cs->b - cs->a);
    double y2 = 2.0 * y;

    double e = 0.0;

    for(j = cs->order; j>=1; j--)
    {
        double temp = d;
        d = y2*d - dd + cs->c[j];
        e += fabs(y2*temp) + fabs(dd) + fabs(cs->c[j]);
        dd = temp;
    }

    { 
        double temp = d;
        d = y*d - dd + 0.5 * cs->c[0];
        e += fabs(y*temp) + fabs(dd) + 0.5 * fabs(cs->c[0]);
    }

    result->val = d;
    result->err = MATH_DBL_EPSILON * e + fabs(cs->c[cs->order]);

    return MATH_SUCCESS;
}