double bessk(int n,double x)
{
	int j;
	double tox,bkm,bk,bkp,temp;
    if( n < 2)
	{
        cout<<"bad argument n in bessk";
        _c_exit();
    }
    tox = 2.0 / x;
    bkm = bessk0(x);
    bk = bessk1(x);
    for( j = 1;j<=n-1;j++)
	{
        bkp = bkm + j * tox * bk;
        bkm = bk;
        bk = bkp;
    }
    temp = bk;
	return temp;
}