mirror of https://github.com/Gnucash/gnucash
But put it in app-utils where it's used and load it explicitly.pull/284/head
John Ralls
8 years ago
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923995f2cc
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;; This program is free software; you can redistribute it and/or
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;; modify it under the terms of the GNU General Public License as
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;; published by the Free Software Foundation; either version 2 of
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;; the License, or (at your option) any later version.
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;;
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;; This program is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;;
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;; You should have received a copy of the GNU General Public License
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;; along with this program; if not, contact:
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;;
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;; Free Software Foundation Voice: +1-617-542-5942
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;; 51 Franklin Street, Fifth Floor Fax: +1-617-542-2652
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;; Boston, MA 02110-1301, USA gnu@gnu.org
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;; Financial functions originally used by the mortgage/loan druid,
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;; but useful in scheduled transactions
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;;
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;; Copyright 2002 Joshua Sled <jsled@asynchronous.org>
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;; Update 2012 Frank H. Elenberger <frank.h.ellenberger@gmail.com>
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;;
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;; Simple function for testing:
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(define (gnc:foobar val) val)
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;; pretty literal copies of similar code from gnumeric-1.0.8, except we want
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;; positive values to be returned (as gnucash will handle the credit/debit
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;; appropriately)
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;; interest payment amount:
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(define (gnc:ipmt rate per nper pv fv type)
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(* -1 (* rate
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(- 0 (calc-principal pv
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(calc-pmt rate nper pv fv type)
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rate (- (if (> per nper) nper per) 1)))))
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)
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;; principal payment amount:
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(define (gnc:ppmt rate per nper pv fv type)
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(let* ((pmt (calc-pmt rate nper pv fv type))
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(ipmt (gnc:ipmt rate per nper pv fv type)))
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(* -1 (- pmt (* -1 ipmt))))
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)
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;; payment amount:
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(define (gnc:pmt rate nper pv fv type)
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(* -1 (calc-pmt rate nper pv fv type))
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)
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;; 2 functions from
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;; http://lists.gnucash.org/pipermail/gnucash-user/2005-February/012964.html
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;; future value of deposits with compound interests:
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(define (gnc:futureValue a r n t)
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;; Parameters:
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;; a: amount
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;; r: interest rate
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;; n: frequency per year
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;; t: time
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;;
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;; formula from http://www.riskglossary.com/articles/compounding.htm
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(* a (expt (+ 1 (/ r n)) (* n t))))
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(define (gnc:computeInterestIncrement amount interest periods i)
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(let ((thisVal (gnc:futureValue amount interest periods i))
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(prevVal (gnc:futureValue amount interest periods (- i 1))))
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(- thisVal prevVal)
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)
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)
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;;;;;
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;; below: not-exposed/"private" functions, used by the "public" functions
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;; above.
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;;;;;
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(define (calc-pmt rate nper pv fv type)
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(let ((pvif (calc-pvif rate nper))
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(fvifa (calc-fvifa rate nper)))
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(/ (- (* (- 0 pv) pvif) fv)
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(* fvifa
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(+ 1.0
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(* rate type)))))
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)
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(define (calc-pvif rate nper)
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(expt (+ 1 rate) nper)
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)
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(define (calc-fvifa rate nper)
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(/ (- (expt (+ 1 rate) nper) 1) rate)
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)
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(define (calc-principal pv pmt rate per)
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(+ (* pv (expt (+ 1.0 rate) per))
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(* pmt (/ (- (expt (+ 1 rate) per)
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1)
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rate)))
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)
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;; This section added in 2005. Ludovic Nicolle
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;; Formula to get the rate for a given period if there are yper in the year
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;; And the official rate is compounded ycomp in the year.
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;; For example, a mortgage being monthly has yper = 12
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;; and if the posted rate is a plain annual rate, then ycomp = 1.
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;; but if the posted rate is compounded semi-annually, as is the case in Canada,
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;; then ycomp = 2.
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;; this function can be used to enter the nominal rate in the formulas, without
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;; pre-calculating the power function below.
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(define (gnc:periodic_rate rate yper ycomp)
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(- (expt (+ 1.0 (/ rate ycomp)) (/ ycomp yper) ) 1.0)
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)
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;; the three following functions with prefix gnc:cpd_ are more generic
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;; equivalents of gnc:pmt, gnc:ipmt and gnc:ppmt above, with some differences.
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;; First difference is that they take the annual nominal rate and two yearly
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;; frequencies: rate is annual, not per period (the functions calculate it
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;; themselves) yfreq determines the compounding frequency of the payed/charged
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;; interest ycomp determines the compounding frequency of the annual nominal
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;; rate
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;; Second difference is for rounding. My experience shows that all banks do not
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;; use the exact same rounding parameters. Moreover, on top of that situation,
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;; numerical calculations in gnucash using the original gnc:pmt, gnc:ipmt and
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;; gnc:ppmt functions above can also create another set of rounding issues. Both
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;; problems create the "odd-penny imbalance" problem.
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;; So the gnc:cpd_Zpmt functions do automatic rounding, the goal being to have
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;; PPMT = PMT - I holding true for all calculated numbers. However, this won't
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;; fix the first problem if your bank can't do proper maths and manual fixing of
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;; transactions will still be required.
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;; FIXME: One problem with the rounding procedure in these three functions is
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;; that it is always rounding at the second decimal. This works great with
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;; dollars and euros and a lot of major currencies but might well cause issues
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;; with other currencies not typically divided in 100. I have not tested
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;; anything else than dollars.
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;; If the automatic rounding causes issues for a particular case, one can always
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;; use the equivalence of the cpd_ and non-cpd_ functions, by using
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;; periodic_rate() like this: gnc:cpd_pmt( rate:yfreq:ycomp :nper:pv:fv:type) is
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;; equivalent to gnc:pmt(periodic_rate(rate:yfreq:ycomp):nper:pv:fv:type)
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;; On the opposite side, if you want the automatic rounding but don't understand
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;; how to use the cpd_ functions, here is a quick example on how to convert
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;; original gnc:Zpmt function calls. The typical setup is to use 'rate/yfreq' as
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;; the first parameter, so the solution is to simply use yfreq for both yfreq
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;; and ycomp in the gnc:cpd_Zpmt calls, like this: gnc:pmt( rate / yfreq
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;; :nper:pv:fv:type) is equivalent to gnc:cpd_pmt( rate:yfreq:yfreq
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;; :nper:pv:fv:type)
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(define (gnc:cpd_ipmt rate yfreq ycomp per nper pv fv type)
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(* 0.01
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(round
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(* -100 (* (gnc:periodic_rate rate yfreq ycomp)
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(- 0 (calc-principal pv
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(calc-pmt (gnc:periodic_rate rate yfreq ycomp) nper pv fv type)
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(gnc:periodic_rate rate yfreq ycomp) (- per 1))))
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)
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)
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)
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)
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(define (gnc:cpd_ppmt rate yfreq ycomp per nper pv fv type)
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(let* (
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(per_rate (gnc:periodic_rate rate yfreq ycomp))
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(pmt (* -1 (gnc:cpd_pmt rate yfreq ycomp nper pv fv type)))
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(ipmt (* per_rate (calc-principal pv pmt per_rate (- per 1))))
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)
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(
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* -1 (+ pmt ipmt)
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)
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)
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)
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(define (gnc:cpd_pmt rate yfreq ycomp nper pv fv type)
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(* 0.01
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(round
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(* -100
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(calc-pmt (gnc:periodic_rate rate yfreq ycomp) nper pv fv type)
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)
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)
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)
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)
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