[GNC] Loan Mortgage repayment assistant problem

[David Carlson]

John,

Thanks for the reference.  Alas, I will need to do some homework to
properly read SCM.  There must still be some sort of rounding issue
creeping in if the Scheduled Transaction SLR sometimes generates an
imbalance from ppmt = pmt - ipmt.

David C

On Tue, Jan 8, 2019 at 3:44 PM John Ralls <jralls at ceridwen.us> wrote:

> The thee functions are defined in
> https://github.com/Gnucash/gnucash/blob/maint/libgnucash/app-utils/fin.scm,
> prefixed with gnc: (so gnc:ipmt etc.).
>
> At line 41ff you'll see that ppmt = pmt - ipmt.
>
> Regards,
> John Ralls
>
>
> > On Jan 8, 2019, at 12:48 PM, David Carlson <david.carlson.417 at gmail.com>
> wrote:
> >
> > My point is that the equations are defined by the assistant, and I think
> that they can be expressed in a form that concentrates all the errors into
> one line where a simple rounding would not generate a problem where the
> parts do not add up to 100%.  Granted, the errors may sometimes cause
> inaccurate results, but they would not add the imbalance line to the
> transaction.
> >
> > The current equations are three  evaluations called pmt(numbers),
> ppmt(numbers) and ipmt(numbers) with no clue how they are actually
> evaluated.
> >
> > Apparently pmt is not always the sum of ppmt and ipmt. when rounding
> happens.  If ipmt were expressed as pmt-ppmt, there would be no imbalance,
> but one of the other two ways to express all three may be less likely to
> generate inaccurate results.
> >
> > David C
> >
> > On Mon, Jan 7, 2019 at 10:19 PM John Ralls <jralls at ceridwen.us> wrote:
> >
> >
> > > On Jan 7, 2019, at 3:14 PM, David Carlson <david.carlson.417 at gmail.com>
> wrote:
> > >
> > > I just had a scheduled transaction that was set up by the loan/mortgage
> > > repayment assistant appear with 0.01 Imbalance-USD.
> > >
> > > I would think that GnuCash should have an accuracy method that would
> > > prevent this from happening.  Is this a bug?
> > >
> > > I am using GnuCash 2.6.17 in Ubuntu 16.04 today.
> >
> > The accuracy method is what created the imbalance entry. ;-)
> >
> > There’s nothing in the SX system to pre-instantiate future scheduled
> transactions and ensure that they’re balanced. What would you have the
> check function do if it found an imbalanced case? How would you handle
> variables whose values are set by the user in the SLR dialog?
> >
> > Regards,
> > John Ralls
> >
>
>