Newbie migration issues

[Josh Sled]

On Sat, 2005-01-29 at 01:05, Rod Engelsman wrote:

> I go into the Loan Druid. On the first screen I enter 8183.47 in the 
> "Amount" box. Loan account is "Liabilities:Loan:Student Loan". Interest 
> rate 3.125%. Type is "Fixed". Start date 2/20/2005. Length is 476 months 
> (calculated by the Financial Calculator). Months remaining says 476 as 
> well. Hit "Next".
> Skip all the Mortgage options because they don't apply. Next screen 
> says: Name = Loan, Amount = pmt( 0.03125 / 12 : 476 : 8183.47 : 0 : 0 ). 
> Payment from, principal to, and Interest to is all correct. Repayment 
> frequency is monthly, start date 2/20/2005. Hit "Next".
[deletia]
> Obviously, this amortization schedule is way screwed up. So what did I 
> do wrong?

Yeah, quite screwed up.

 can only get 476 months when I use the financial calculator entering...

* Interest Rate: 3.125
* Present Value: 8183.47
* Periodic Payment: -30
* Future value: 0

...but since the future value isn't $0 -- since there's another 116
months of payments -- that's simply user-error on your part.

The last two parameters of the `pmt(...)` formula are "future value" and
"type" [type = payments at beginning or end of period]; you could
manually edit the SX after the fact to get the correct future value of
the account [8183.47 - 11*30, assuming no interest accumulates which it
probably does...]; then it's be 11 payments [not 476], and it should
calculate the correct principle/interest amounts...  Of course, you'll
need to setup another Loan SX after those 11 payments to account for the
change, since as Derek points out the loan druid can't yet handle that.

That all assumes that the basic computations are correct ... 

I can't seem to reproduce the computations described above in any way
... with 11 payments, it believes that the FV is 0, and thus computes
payments of ~$755.  With 476 payments, it correctly computes payments of
$30 [plus $0.01, unfortunately].  There's the other bug you described,
but I'm not sure _how_ this occurs.  If you find `fin.scm`, you'll see
that the calculations being done -- as one would expect -- are about as
simple as any.


Obviously, the loan druid should be better, in many ways.  I ran out of
time; more recently, when I've found time to work on GnuCash again,
there are more pressing concerns [gnome2 port], the resolution of which
has a higher priority, and in fact will help set-up the playing field so
that I can -- for instance -- re-write the formula expression parser. 
Which would make it easier to have, say, a first-class formula editor,
that could say "hey, user, this 4th argument is the 'future value'
parameter".  Or to support variable- and piecewise- loan-repayment
schedules.  Or using the actual account-balance rather than the
idealized form of the loan payment.

So, you can help in a variety of ways, or you can not use the software
or whatever. But your current attitude of complaining while
simultaneously asking for support doesn't really make me want to help
you.

...jsled

-- 
http://asynchronous.org/ - `a=jsled; b=asynchronous.org; echo ${a}@${b}`