static public double ppmt(double r, int per, int nper, double pv) {return pmt(r, nper, pv) - ipmt(r, per, nper, pv);}

static public double PPMT(double r, int per, int nper, double pv){return PMT(r, nper, pv) - IPMT(r, per, nper, pv);}
