Based on period interest rate, number of periods, and loan amount, this function calculates
the repayment of the loan such that it would be paid off fully at the end of the loan.
This function is designed to be equivalent to the Excel function PMT.
It calculates based on a fixed interest rate, FV=0, and charging is
at the end of the period. Response is rounded to 2dp
Usage
PMT(rate, nper, pv)
Arguments
rate
The nominal interest rate per period (should be positive)
nper
Number of periods
pv
Present value i.e. loan advance (should be positive)
PMT(0.1,12,3000) # =-440.29 taken from exceldf<-data.frame(rate=c(.1,.2),nper=c(12,24),pv=c(3000,1000))
PMT(df$rate,df$nper,df$pv) # =-440.29,-202.55 taken from excel