# \[ANN\] New registered package Chevie

**URL:** <https://discourse.julialang.org/t/ann-new-registered-package-chevie/107683>\
**Category:** Package Announcements\
**Tags:** package, announcement, math, algebra\
**Created:** [December 15, 2023, 6:48pm UTC](https://discourse.julialang.org/t/ann-new-registered-package-chevie/107683 "2023-12-15T18:48:35Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Jean\_Michel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jean_michel/32/8282_2.png) [@Jean\_Michel](https://discourse.julialang.org/u/Jean_Michel)\
**Post date:** [December 15, 2023, 6:48pm UTC](https://discourse.julialang.org/t/ann-new-registered-package-chevie/107683/1 "2023-12-15T18:48:35Z")

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This to announce a new registered package `Chevie` dealing with various areas of representation theory.  
[https://github.com/jmichel7/Chevie.jl](https://github.com/jmichel7/Chevie.jl)

Here is the README  
This is my attempt to port the Chevie package from GAP3 to Julia. I started  
this project at the end of 2018 and it is still in flux so some function  
names or interfaces may still change. Pull requests and issues are welcome.

I have implemented the GAP functionality (infrastructure) needed to make  
Chevie work. I have already registered most of this infrastructure as  
separate packages; the following packages are loaded and re-exported so  
that their functionality is automatically available when you use `Chevie`.  
In other words, `Chevie` is a meta-package for the following packages:

- (univariate) [LaurentPolynomials](https://github.com/jmichel7/LaurentPolynomials.jl) (and rational fractions)
- (multivariate) [PuiseuxPolynomials](https://github.com/jmichel7/PuiseuxPolynomials.jl) (and rational fractions when there are no fractional exponents)
- [CyclotomicNumbers](https://github.com/jmichel7/CyclotomicNumbers.jl)(elements of cyclotomic fields)
- [ModuleElts](https://github.com/jmichel7/ModuleElts.jl) (elements of a free module over some ring)
- [Combinat](https://github.com/jmichel7/Combinat.jl) (combinatorics and some basic number theory)
- [PermGroups](https://github.com/jmichel7/PermGroups.jl) (permutations, groups, permutations groups. It contains the modules `Perms` and `Groups` which could be separate packages)
- [SignedPerms](https://github.com/jmichel7/SignedPerms.jl) (signed permutations)
- [MatInt](https://github.com/jmichel7/MatInt.jl) (Integer matrices and lattices)
- [CycPols](https://github.com/jmichel7/CycPols.jl) (cyclotomic polynomials)
- [GenLinearAlgebra](https://github.com/jmichel7/GenLinearAlgebra.jl) (linear algebra on any field/ring)
- [FinitePosets](https://github.com/jmichel7/FinitePosets.jl) (finite posets)
- [FiniteFields](https://github.com/jmichel7/FiniteFields.jl) (finite fields)
- [GroupPresentations](https://github.com/jmichel7/GroupPresentations.jl) (presentations of groups, and groups defined by generators and relations)
- [UsingMerge](https://github.com/jmichel7/UsingMerge.jl) (Automatically compose several packages)

Have a look at the documentation of the above packages to see how to use  
their features. I have implemented some other infrastructure which  
currently resides in `Chevie` but may eventually become separate packages:

- factorizing polynomials over finite fields (module `FFfac`)
- factorizing polynomials over the rationals (module `Fact`)
- Number fields which are subfields of the Cyclotomics (module `Nf`)

For permutation groups I have often replaced GAP’s sophisticated algorithms  
with naive but easy-to-write methods suitable only for small groups  
(sufficient for the rest of the package but perhaps not for your needs).  
Otherwise the infrastructure code is often competitive with GAP, despite  
using much less code (often 100 lines of Julia replace 1000 lines of C);  
and I am sure it could be optimised better than I did. Comments on code and  
design are welcome. For functions that are too inefficient or difficult to  
implement (such as character tables of arbitrary groups), `Chevie` uses the  
`GAP` package as an extension. This means that if you have the `GAP`  
package installed, `Chevie` will automatically call GAP4 to implement these  
functions. The code in this package is often 10 times faster than the  
equivalent GAP3 Chevie code (after the maddeningly long compilation time on  
the first run — Julia’s TTFP).

The `Chevie` package currently contains about 95% of the GAP3/Chevie  
functionality, ported from Gap3. If you are a user of GAP3/Chevie, the  
`gap` function can help you to find the equivalent functionality in  
`Chevie.jl` to a Gap3 function: it takes a string and gives you Julia  
translations of functions in Gap3 that match that string.

```julia-rep1
julia> gap("words")
CharRepresentationWords => traces_words_mats
CoxeterWords(W[,l]) => word.(Ref(W),elements(W[,l]))
GarsideWords => elements

```

You can then access online help for the functions you have found.

The port to Julia is not complete in the sense that 80% of the code is the  
data library from Chevie, which was automatically ported by a transpiler so  
its code is “strange”. When the need to maintain the `GAP3` and `Julia`  
versions simultaneously subsides, I will do a proper translation of the  
data library, which should give an additional speed boost.

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<div class="post-metadata">

**Author:** ![Syx\_Pek](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/syx_pek/32/6364_2.png) [@Syx\_Pek](https://discourse.julialang.org/u/Syx_Pek)\
**Post date:** [February 13, 2024, 2:09am UTC](https://discourse.julialang.org/t/ann-new-registered-package-chevie/107683/2 "2024-02-13T02:09:08Z")

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This is the one package I use everyday, this and Oscar.jl are perhaps the most important packages in my workflow.

Thanks again for this!