Changelog

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1.0.0 — 2026-07-04

A complete rewrite of the library. Breaking changes — some return values differ from 0.x because intermediate rounding was removed and the solver was replaced, and errors are now atoms rather than strings.

Rate of return

  • xirr/1,2,3 and xirr! — internal rate of return for dated cash flows, given as {date, amount} pairs or two parallel lists. Dates may be Date structs or {year, month, day} tuples.
  • irr/1,2 and irr! — internal rate of return for periodic (equally spaced) flows.
  • mirr/3,4 and mirr! — modified internal rate of return.
  • Newton-Raphson solver with an analytic derivative, a bracketing bisection fallback, and a hard iteration cap.

Present / future value

  • xnpv/2,3 and xnpv! — net present value of dated cash flows.
  • npv/2,3 and npv! — net present value of periodic flows. The first amount sits at period 0 (so npv(irr(a), a) ≈ 0), which differs from spreadsheet NPV (first amount at period 1).

Time value of money

  • fv/5, pv/5, pmt/5, nper/5, rate/6 and their ! variants — solve the annuity equation for one unknown, with annuity-due (type: 1) support.

Depreciation

  • sln/3, syd/4, ddb/5, db/5 and their ! variants — straight-line, sum-of-years'-digits, double-declining and fixed-declining depreciation.

Amounts and options

  • Amounts may be integers, floats, or Decimal values (via the optional decimal dependency); results are always floats.
  • Options (:guess, :tolerance, :max_iterations, :precision) are validated with nimble_options; unknown keys and out-of-type values raise.

Removed

  • The timex runtime dependency (now uses the standard-library Date).
  • The spawn_link-per-cash-flow "parallel" mapping, which was slower and unsafe.

Tooling

  • Requires Elixir ~> 1.18; tested on Elixir 1.18/OTP 27 and 1.20/OTP 29.
  • Travis CI replaced with GitHub Actions.