Hi David,
I have one suggestion for the haddocks. I made a solid effort to wade into
the explanation of branch cuts and negative zeros, but I never managed to
figure out why I should care. ;) In other words: tl;dr.
Would it be possible to write a pithy few words right at the beginning as
an introduction that motivates the topic? If, as you say, few other
languages take the subject into account, it's very likely that few
programmers take it into account either.
In general, as a math-conscious member of the community, I'm happy to see
this kind of work being accomplished, so thanks!
-Bryan
On Fri, 22 Oct 2021, 17.48 David James,
Hi all – I now have fixes for all the issues I’m aware of. However, it’s quite possible I’ve made a mistake somewhere (either in the new code or the testing), so if anyone would like to help review either please let me know.
*Group 1 issues* (real numbers in Windows, where the defects are in mingw-w64: I’ve raised issue #20424 https://gitlab.haskell.org/ghc/ghc/-/issues/20424 for this. The fixes (commits 66ba5f32 https://github.com/mingw-w64/mingw-w64/commit/66ba5f3221c786de24f5fc4b9c0236... and 021dffb8a https://github.com/mingw-w64/mingw-w64/commit/021dffb8a482eb9d1b39569cd1ea42...) have been made in mingw-w64 and are getting integrated into Haskell soon.
*Group 2 issues* (complex numbers, where the defects are in Complex.hs). I’ve raised issue #20425 https://gitlab.haskell.org/ghc/ghc/-/issues/20425 for this and have the code fixes here https://gitlab.haskell.org/davjam/ghc/-/blob/ComplexBranchCuts/libraries/bas.... The new code changes many of the functions (I’ve given examples in the issue) and adds a few. I’ve also put the Haddock output here https://davjam.github.io/HaskellNumericsTestsFixes/TrigDiags/Data-Complex.ht.... (It now defines and gives an explanation of the branch cuts). I’ve also put some diagrams here https://davjam.github.io/HaskellNumericsTestsFixes/TrigDiags/Curr.html illustrating some of the problems.
I’ve done about as much testing as I can think of, using the code here https://github.com/davjam/HaskellNumericsTestsFixes/blob/main/ComplexTests.h.... Ideally I’d bulk-test against a reliable independent source, but can’t find one. AFAICT WolframAlpha https://www.wolframalpha.com/input/?i=sin%28-0.0%29, Excel, gnumeric, CLISP don’t support negative zeros. Python https://www.python.org/ seems to, but cmath has incorrect branch cuts (cmath.sqrt(-4-0j) gives 2j). Matlab https://www.advanpix.com/2016/04/28/branch-cuts-and-signed-zeros-in-matlab/ also seems deficient in a number of areas. (Hmmm: maybe no one cares about these working correctly??)
Sorry about the delay in sending this, David.
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