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 #Future value interest factor of annuities, FIXME: this sucks for very small rates
    return(-((pv * pvif) + pmt * (1.0 + rate * type) * fvifa))
}

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 #Future value interest factor of annuities, FIXME: this sucks for very small rates
    return((-fv - pmt * (1.0 + rate * type) * fvifa) / pvif)
}