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export function PMT (rate, nperiod, pv, fv, type) {
if (!fv) fv = 0
if (!type) type = 0
if (rate == 0) return -(pv + fv)/nperiod
const pvif = Math.pow(1 + rate, nperiod)
let pmt = rate / (pvif - 1) * -(pv * pvif + fv)
if (type) {
pmt /= (1 + rate)
}
return pmt
}
function IPMT(pv, pmt, rate, per) {
const tmp = Math.pow(1 + rate, per)
return 0 - (pv * tmp * rate + pmt * (tmp - 1))
}
export function PPMT(rate, per, nper, pv, fv, type) {
if (per < 1 || (per >= nper + 1)) return null
const pmt = PMT(rate, nper, pv, fv, type)
const ipmt = IPMT(pv, pmt, rate, per - 1)
return pmt - ipmt
}
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