[GRASS-git] [OSGeo/grass] c7928b: r.univar: Use Kahan sum to avoid floating point er...

[Chung-Yuan Liang]

  Branch: refs/heads/main
  Home:   https://github.com/OSGeo/grass
  Commit: c7928beda9aad46a8375ef45a9e910377aa00811
      https://github.com/OSGeo/grass/commit/c7928beda9aad46a8375ef45a9e910377aa00811
  Author: Chung-Yuan Liang <77927944+cyliang368 at users.noreply.github.com>
  Date:   2025-05-24 (Sat, 24 May 2025)

  Changed paths:
    M python/grass/gunittest/testsuite/test_assertions.py
    M raster/r.mfilter/testsuite/test_r_mfilter.py
    M raster/r.neighbors/testsuite/test_r_neighbors.py
    M raster/r.resamp.filter/testsuite/test_r_resamp_filter.py
    M raster/r.resamp.interp/testsuite/test_r_resamp_interp.py
    M raster/r.texture/testsuite/test_rtexture.py
    M raster/r.texture/testsuite/test_rtexture_parallel.py
    M raster/r.univar/r.univar_main.c
    A raster/r.univar/testsuite/test_r_univar_parallel.py

  Log Message:
  -----------
  r.univar: Use Kahan sum to avoid floating point errors (#5750)

Univar sums values across large amounts of numbers, so the floating point errors could be huge if a naive sum is applied.

This PR introduces Kahan sum to solve this problem in `r.univar`. The testing reference numbers derived from the previous `r.univar` implementation are also updated.

* modify the precision and some wrong reference numbers

* set the precision requirement to 1e-10

* use KahanSum and create test for multithreads

* make sure the calculation/output match the raster type

* update testing reference based on corrected numbers

* use lower case and underscore for the function name

* simplify the testing script of r.univar parallel

* update reference numbers in testing files

* make kahan some as a static fucntion, move the function body to the bottom

* update reference number for testing

* remove unused comment

---------

Co-authored-by: Māris Nartišs <maris.gis at gmail.com>



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