alexjansons opened a new pull request, #733: URL: https://github.com/apache/poi/pull/733
## Summary This PR resolves 2 issues in the MIRR function implementation: - formula calculation issue - input parameter order ## Formula Calculation Issue The current MIRR implementation produces inaccurate results due to an error in the present value calculation. Let's take an example from Wikipedia: [Modified internal rate of return](https://en.wikipedia.org/wiki/Modified_internal_rate_of_return) Input data: > Cash flow values: -1000, -4000, 5000, 2000 Finance rate: 10% Reinvestment rate: 12% Calculation result: - Output from current MIRR implementation: 20.57% - Expected output based on Wikipedia example: 17.91% The discrepancy appears due to including finance and reinvestment rates in the present value calculation. Only the finance rate should be considered. Here is a related code fragment: ```java if (anIn < 0) { pv += anIn / Math.pow(1 + financeRate + reinvestRate, indexN++); } ``` ## Input Parameter Order The current implementation uses a non-standard order for finance and reinvestment rates, unlike common spreadsheet applications (Excel, Google Sheets). Current order: (values, reinvestRate, financeRate). Proposed order: (values, financeRate, reinvestRate). I.e. to calculate the MIRR for the formula mentioned above one have pass the following values to `Mirr#evaluate(double[] values)` function: `-1000D, -4000D, 5000D, 2000D, 0.12D, 0.1D` however more the order according to most popular spreadsheet applications would be: `-1000D, -4000D, 5000D, 2000D, 0.1D, 0.12D` ## Testing A test from Wikipedia has been added to verify the formula accuracy. All other tests are left intact except for parameter order. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: dev-unsubscr...@poi.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@poi.apache.org For additional commands, e-mail: dev-h...@poi.apache.org
