mathmatical expressions evaluation

[John Machin]

Paul McGuire wrote:
> Here's
> a simple loan amortization schedule generator:
>
> def amortizationSchedule( principal, term, rate ):
>     pmt = ( principal * rate * ( 1 + rate)**term ) / (( 1 +
rate)**term - 1)

Simpliciter:
pmt = principal * rate / (1 - (1 + rate)**(-term))

>     pmt = round(pmt,2)  # people rarely pay in fractional pennies
>     remainingPrincipal = principal
>     for pd in range(1,term+1):
>         if pd < term:
>             pdInterest = rate * remainingPrincipal
>             pdInterest = round(pdInterest,2)
>             pdPmt = pmt
>         else:

Huh? You don't charge interest in the last period? I'd like to apply
for a loan of $1B for a term of one month with monthly repayments.

>             pdInterest = 0
>             pdPmt = remainingPrincipal
>         pdPrincipal = pdPmt - pdInterest
>         remainingPrincipal -= pdPrincipal
>         yield pd, pdPmt, pdInterest, pdPrincipal, remainingPrincipal
>