[GNC] Loan Mortgage repayment assistant problem

[Christopher Lam]

Well the SCM has numerous references to "round" and "rounding errors" so 
it's to be expected.

Please file a bug with example numbers, and hopefully these errors may 
be fixed.

On 9/1/19 7:35 am, David Carlson wrote:
> 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
>>>
>>
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