[SLUG] project

[Stephen O'Neill]

Bob Garrood wrote:
> # A is for amount borrowed, n for number of years and i the annual interest 
> rate.
> m=n*12
> r=(1+i/1200)
> p=A*r^(m-1)*(r-1)/(r^m-1)
> {print p}
> #   This assumes that the rate charged per month is 1/12th the annual interest 
> rate, which may not now be true.

Hi Bob,

That solution is really neat - and certainly not something that I would 
have imagined AWK capable of. I thought that AWK was just for text 
stream processing....

Re. the formula I will have a look at that in more depth... on my own I 
had got to the point of having:

m = n*12
r = 1 + i/1200

A*(r^m) / (r^m + r^(m-1) + ... + r^0) = Pn

The thing that I didn't know how to express here was Pn without a 
recursive loop for the sum - which seems to be what your formula solves.

I'll study your solution until I understand what it does.

Re. the rate charged per month. Interest is calculated daily so differs 
for each month (which I want to account for in my spreasheet). Although 
using equal monthly rates will still give a good approximation.

So to get the monthly rate we take:

y for number of days in year, d for number of days in month, i for 
annual rate:

r = (1 + (i/y) / 100) ^ d

This means that you immediately need programming for accuracy, but I 
will revisit factoring that into the method you gave me.

The thing here for me is do I want a quick solution or an accurate 
solution. And given that there's a bug in my solution as it is I suspect 
that I want the quick solution.

Anyway, I'm sorry for, as a great philosopher once wrote, "waving my 
ignorance around for all to see".

Oh, and MathML in HTML anybody?

Cheers for the help,

Steve O


		
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