excel中ppmt/pmt/ipmt的计算方式

参考来源： https://www.experts-exchange.com/articles/1948/A-Guide-to-the-PMT-FV-IPMT-and-PPMT-Functions.html

pmt计算公式：

1 double pmtdouble r, int nper, double pv, double fv, int type) {
2         double pmt = r / Math.pow1 + r, nper) - 1)
3                 * -pv * Math.pow1 + r, nper) + fv);
4 
5         return pmt;
6     }

ppmt计算公式：

double ppmtdouble r, int per, int nper, double pv, double fv, int type) {
        return pmtr, nper, pv, fv, type) - ipmtr, per, nper, pv, fv, type);
    }

ipmt计算公式

1 double ipmtdouble r, int per, int nper, double pv, double fv, int type) {
2 
3         double ipmt = fvr, per - 1, pmtr, nper, pv, fv, type), pv, type) * r;
4 
5         if type == 1) ipmt /= 1 + r);
6 
7         return ipmt;
8     }

fv计算公式：

double fvdouble r, int nper, double c, double pv, int type) {
        double fv = -c * Math.pow1 + r, nper) - 1) / r + pv
                * Math.pow1 + r, nper));

        return fv;
    }