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

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