fv <- function(rate, nper, pmt, pv = 0.0, type = 0) {
 pvif <- (1+rate)^nper # Present value interest factor
 fvifa <- if(rate==0) nper else ((1+rate)^nper - 1) / rate 
 return(-((pv * pvif) + pmt * (1.0 + rate * type) * fvifa))
  }
fv(rate=0.12, nper=20, pmt=-20000, type=1)
fv(rate=0.01, nper=41, pmt=-100000, type=1)


pv <- function(rate, nper, pmt, fv = 0.0, type = 0) {
  pvif <- (1+rate)^nper # Present value interest factor
  fvifa <- if(rate==0) nper else ((1+rate)^nper - 1) / rate 
  return((-fv - pmt * (1.0 + rate * type) * fvifa) / pvif)
  }
pv(rate=0.07/12, nper=60, pmt=-35000, type=1)
pv(rate=0.18/12, nper=36, pmt=-130149)


pmt <- function(rate, nper, pv, fv=0, type=0) {
  rr <- 1/(1+rate)^nper
  res <- (-pv-fv*rr)*rate/(1-rr)
  return(res/(1+rate*type))
  }
pmt(rate=0.18/12, nper=36, pv=3600000,fv=0, type=0)


fv(rate=0.035/12, nper=c(12,18,24,35,60), pmt=-350000, type=1)
pmt(rate=0.1/12, nper=c(6,12,18,24,36), pv=10000000)