void chebpc(double c[], double d[], int n)
{
    double dd[51];
	int j;
	double sv;
    for (j = 1; j<=n; j++)
	{
        d[j] = 0.0;
        dd[j] = 0.0;
    }
    d[1] = c[n];
    for (j = n - 1; j>=2; j--)
	{
        for ( int k = n - j + 1; k>=2; k--)
		{
            sv = d[k];
            d[k] = 2.0 * d[k - 1] - dd[k];
            dd[k] = sv;
        }
        sv = d[1];
        d[1] = -dd[1] + c[j];
        dd[1] = sv;
    }
    for (j = n; j>=2; j--)
	{
        d[j] = d[j - 1] - dd[j];
    }
    d[1] = -dd[1] + 0.5 * c[1];
}