[GNC] Loan Mortgage repayment assistant problem

[David Carlson]

Absolutely, I was not expecting agreement with the bank, I just think the
creation of an unbalanced transaction is bad form.

David Carlson

On Wed, Jan 9, 2019, 9:03 AM John Ralls <jralls at ceridwen.us wrote:

>
>
> > On Jan 9, 2019, at 6:26 AM, Michael or Penny Novack <
> stepbystepfarm at comcast.net> wrote:
> >
> > On 1/8/2019 11:50 PM, John Ralls wrote:
> >> The answer is probably in app-utils/calculation. All of that was
> probably written before Guile grew a rational number class and I think that
> GncNumerics get converted to doubles before being passed to the interest
> functions. That would pretty much guarantee rounding issues.
> >>
> >> Regards,
> >> John Ralls
> > I will repeat, this sort of "rounding error" is not a bug.
> >
> > If two persons set out to perform a calculation which can be done by a
> number of methods with rounding involved at numerous places and no
> agreement as to either the method to be used or the precision maintained at
> each step THERE IS NO REASONABLE EXPECTATION THAT THEIR ANSWERS WILL MATCH
> EXACTLY.
> >
> > Treated as a "bug", it might* be possible to change the code so as to
> match the answers of a particular lending institution, but then could be
> wrong for another lending institution that used different methods or
> rounding than the first.
> >
> > Michael D Novack    << who in my working days often had to compute the
> "fuzz" for comparisons >>
> >
> > * Might, because you have no reason to suppose that a lending
> institution necessarily used the same methods/rounding for car loans as for
> house mortgages.
>
> Which is why GnuCash mostly uses rational numbers and no rounding for
> internal calculations. Using binary floating-point in financial software is
> a bug on its own, so that “mostly” is a bug. It needs to be “only”.
>
> This isn’t about matching the results with someone else’s computer, this
> is about internal consistency in GnuCash.
>
> Regards,
> John Ralls
>
>
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