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https://issues.apache.org/jira/browse/FINERACT-2809?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18112347#comment-18112347
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Adam Saghy commented on FINERACT-2809:
--------------------------------------
Fix belongs to Xamit Kadirbekov
> FinanicalFunctions.nop() helper: non-zero-rate branch is not the algebraic
> inverse of the adjacent pmt() function
> -----------------------------------------------------------------------------------------------------------------
>
> Key: FINERACT-2809
> URL: https://issues.apache.org/jira/browse/FINERACT-2809
> Project: Apache Fineract
> Issue Type: Improvement
> Affects Versions: 1.15.0
> Reporter: Adam Saghy
> Assignee: Adam Saghy
> Priority: Major
> Fix For: 1.16.0
>
>
> From Xamit Kadirbekov (GERO Research):
> I found a reproducible mathematical defect in the public
> FinanicalFunctions.nop() helper. Its non-zero-rate branch is not the
> algebraic inverse of the adjacent pmt() function.
> Minimal round trip:
> rate = 0.01
> periods = 12
> principal = 1000
> future value = 0
> type = false
> pmt(...) = -88.848788678342
> current nop(...) = 7
> expected nop(...) = 12
> A repository-wide search found no current call site for nop(), so I am
> treating this as a dormant library defect rather than claiming production
> loan impact.
> I prepared a focused correction and regression tests in a public fork:
> [https://github.com/kadyrbekovhamit-cyber/fineract/commit/6980e1377ce2e5a1eaf0586e628b27bb64dd8c26]
> The proposed inverse is:
> A = emiAmount * (type ? 1 + rate : 1)
> growth = (A - rate * futureValue) / (A + rate * principal)
> N = log(growth) / log1p(rate)
> The corrected implementation passes 33/33 direct PMT/NOP round trips across
> zero and non-zero rates, both payment timings, and a non-zero future value. A
> JUnit test is included. The full Gradle target could not run locally because
> this checkout requires JDK 25 while the available JDK is 26.
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