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Magma V2.27 Release Notes

Release notes for Magma V2.27.

46 sections

Introduction

This document provides a terse summary of the new features released as part of Magma versions V2.27 (May 2022).

A small number of new features were exported in patch releases prior to the main release of V2.27 in May 2022 and these are also listed here for completeness. Only significant bugfixes are noted here -- for a more complete list of bugfixes the reader should consult the patch release change log for V2.26-x.

Highlights

Algebraic Geometry

Schemes

  • The function JacobianMatrix (arising out the function IsSingular) has been greatly sped up for certain types of schemes.

Arithmetic Geometry

Curves over Finite Fields

  • A number of optimisations have been made to parts of the Tuitman algorithm for computing zeta functions which substantially improve the performance in many cases.

Arithmetic Fields

Algebraic Number Fields

  • Maximal orders : The computation of all the primes at which an order is not maximal can be an expensive computation when computing maximal orders of number fields due to the expense of factoring large integers. This factorization expense can be reduced by attempting to compute polynomial GCDs over modular rings in a similar way to the Dedekind test combined with coprime factorization which reduces the size of integers to be factored (Sircana, 2020). This approach can also be used in computing maximal orders of orders defined as an extension of another order. While this prefactorization of the discriminant has been available in Magma since V2.26, improvements to the implementation have been made since then, including excluding relative orders defined by a non monic or non integral polynomials from this approach.

    Another approach to reducing the integer factorization cost in computing maximal orders is implemented using the Ramification and Discriminant parameters to the MaximalOrder intrinsic. However, more care needed to be taken when using these parameters with orders defined by a non monic or non integral polynomial.

  • Subfields : It is now possible to test whether a number field is a subfield of another without computing a maximal order. This means that testing whether 2 number fields are isomorphic can now also be done without computing a maximal order. There are a number of algorithms available for computing subfields and the algorithm used for fields of degree over 50 has been changed as it has become faster to compute all roots of the polynomial involved than lifting one root. Computing whether a field is a subfield also installs an embedding of the subfield into the superfield if the field is indeed a subfield. Embeddings can also be added using the Embed intrinsic. It is now checked that the embeddings added using this intrinsic as well as by IsSubfield and IsIsomorphic are consistent with any embeddings previously installed, unless the new Overwrite parameter is set to true when using Embed.

Valuation Rings

  • Valuation rings can be constructed over algebraic number fields and function fields allowing localizations to be computed at ideals of such fields.

Basic Rings

Integer Ring

  • Parallel versions of the ECM and MPQS algorithms for integer factorisation are now available. These are selected by first calling SetNthreads(k); (to select $k$ threads) and optionally the StartWorkers procedure (to select worker nodes) before general integer factorisation is called. (The MPQS algorithm also no longer uses files to communicate between workers.)

Commutative Algebra

Gröbner Bases

  • The parallel version of the Faugere $F_4$ algorithm (selected by SetNthreads) has been greatly improved in the linear algebra phase, while the symbolic reduction and critical pair management phases have been parallelised for the first time. This includes the cases of ideals defined over $\mathrm{GF}(q)$ for $2<q<2^{30}$ where $q$ is not a power of 2 or over $\mathbb{Q}$. New record timings for a 4-core Intel Core i7-7700 CPU (3.60GHz) include the following (for computing the grevlex Gröbner basis in each case):

    • The Cyclic-9 roots ideal over GF(32003): 10.2 secs (4 cores) or 29.3 secs (1 core);

    • The Cyclic-10 roots ideal over GF(32003): 601.2 secs (4 cores) or 1957.1 secs (1 core).

    • The Cyclic-9 roots ideal over $\mathbb{Q}$: 144.3 secs (4 cores) or 286.1 secs (1 core), using 750MB for either computation;

    • The Cyclic-10 roots ideal over $\mathbb{Q}$: 5.2 hours (4 cores) or 16.1 hours (1 core), using 46GB for either computation.

  • The main strategy for the Faugere $F_4$ algorithm has been extended so that by default a limit on the number of critical pairs is now dynamically chosen for each new step (so the pairs limit varies throughout the algorithm). This leads to major speedups for computing Gröbner bases of many types of input ideal for which the previous default strategy of no pairs limit was not optimal.

  • The Faugere $F_4$ has been improved so that the setup of higher-degree critical pairs is delayed as much as possible. As a result, if the final Gröbner basis is trivial or has very small degree polynomials only, the critical pair management is often greatly sped up. The low-level subalgorithm for critical pairs management (used in both the Faugere $F_4$ and Buchberger algorithm) has also been significantly sped up itself in general.

  • The second pass reduction in the linear algebra phase of the Faugere $F_4$ algorithm (which sometimes can be quite expensive) has been significantly sped up.

  • The linear algebra phase of the Faugere $F_4$ algorithm has a new representation for computations over $\mathrm{GF}(p)$ for $p<256$. This yields signifcant memory savings when the Gröbner basis is large, together with a moderate speedup.

  • New functions are provided to create dense MinRank or HFE multivariate polynomial systems.

Ideal Theory

  • The function MinimalBasis for an ideal of a multivariate polynomial ring has been improved in the search for a grading to make the input homogeneous if it is not already. The new function HomogeneousWeightsSearch also does the search for weights.

  • The general strategy for primary decomposition of positive-dimensional ideals has been improved.

Group Theory

Classical Groups

  • In recent years fast methods have been implemented for determining the conjugacy classes of elements in most classical matrix groups. In this version of Magma the coverage of fast conjugacy class construction has been extended to include the following types of group:-

    • Conformal classical groups.

    • The projective versions of the classical groups of these types:-\ $GL$, $SL$\ $Sp$\ $GU$, $SU$\ $GO+$, $SO+$, $Omega+$\ $GO-$, $SO-$, $Omega-$\ $GO$, $SO$, $Omega$.

Finite Soluble Groups

  • New routines for construction of finite soluble groups are much faster when the group order has large prime divisors.

  • A new algorithm for automorphism groups of finite nilpotent groups has been implemented.

Databases of Groups

  • The small groups database has been expanded to include all groups with order a product of at most 4 primes. This implements the catalogue of Dietrich, Eick and Pan.

Lattices and Quadratic Forms

Lattices

  • An effective parallel version of close vector enumeration in lattices was completed. (V2.26-4)

  • The FP-based LLL algorithm has been parallelised (selected by SetNthreads) so that non-trivial speedups are achieved for lattices with medium dimension and large integer entries (occurring in several computations in number theory and in modular reconstruction algorithms).

Linear Algebra and Module Theory

Linear Algebra over $\mathbb{Z}$

  • The algorithm for final saturation when computing the nullspace of a matrix over $\mathbb{Z}$ has been improved.

  • The general algorithm for saturation of an integral lattice has been improved.

Representation Theory

$KG$-Modules

  • The computation of irreducible $G$-modules in characteristic zero for a pc-group $G$ has been made more stable.

  • The main algorithm for the computation of irreducible $G$-modules in characteristic zero has been improved, particularly in the case that the composition length of $G$ is non-trivial.

System

Parallelism

  • There is a new procedure StartWorkers to start up Magma worker jobs remotely without having to start up Magma jobs on remote machines manually. This is useful for the internal distributed algorithms (such as code/lattice enumeration, integer factorisation). As a result, the -w command line option is no longer needed unless more manual control is desired.

Aggregates and Mappings

Bug Fixes:

  • Error messages which may arise from some preimage computations for rule maps have been improved. (V2.26-7)

Algebraic Geometry

Schemes

New Features:

  • The function JacobianMatrix (arising out the function IsSingular) has been greatly sped up for certain types of schemes.

Algebraic Curves

Bug Fixes:

Arithmetic Geometry

Curves Over Finite Fields

New Features:

  • A number of optimisations have been made to parts of the Tuitman algorithm for computing zeta functions which substantially improve the performance in many cases.

Bug Fixes:

  • A bug in the Tuitman algorithm for computing zeta functions related to precision has been fixed. (V2.26-7)

Arithmetic Geometry (Modular Forms)

Modular Forms

Bug Fixes:

  • The function eq for modular form elements has been made consistent with IsZero.

  • The function Newforms has been sped up for moderately-size cusp form spaces.

Bug Fixes:

  • ClassicalModularPolynomial(1) has been fixed so it returns the symmetric polynomial $x-y$. (V2.26-10)

  • An occasional crash in computing the dimension of Hilbert cusp form spaces has been fixed. (V2.26-11)

  • A slowdown in computing Hecke operators of cusp form spaces has been fixed. (V2.26-11)

Arithmetic Fields (Global)

Algebraic Number Fields

New Features:

  • The Localization of an order of a number field at an ideal of that order can now be computed. A valuation ring is returned.

  • Whether warnings regarding expensive class group computations are printed can now be controlled using SetPrintClassGroupWarnings.

Changes and Removals:

  • The efficiency of the Montes algorithm as been improved in one place.

Bug Fixes:

  • A bug has been fixed when computing a ClassGroup of a degree 2 field. (V2.26-4)

  • The prefactorization of discriminants when computing a MaximalOrder over the integers has been improved. (V2.26-4, V2.26-7)

  • The computation of first roots of elements of number fields is now handled as a trivial case. (V2.26-7)

  • A bug when inverting elements of low-degree number fields where the defining polynomial has large integer coefficients has been fixed. (V2.26-7)

  • The test for a number field being a subfield of another (intrinsic IsSubfield) no longer involves computing a maximal order. (V2.26-7)

  • The test for a two number fields being isomorphic (intrinsic IsIsomorphic) no longer involves computing a maximal order. (V2.26-7)

  • An improvement has been made when UsePowerProduct is true when computing PicardGroup. The expansion of large powers is further avoided. (V2.26-7)

  • A check that the unit rank is at most 10 has been added to ExceptionalUnits. (V2.26-7)

  • A crash in MaximalOrder for number fields which involve a non-monic or non integral defining polynomial has been fixed. (V2.26-9)

  • The embeddings of number fields using Embed, subset, IsSubfield and IsIsomorphic have been improved. Now, once an embedding has been added, no embedding that is inconsistent with it can be added, except using Embed with the new Overwrite parameter set to true. (V2.26-10)

  • Magma level printing of towers of algebraic number fields has been fixed. (V2.26-11)

  • The algorithm used to compute IsSubfield for fields of degree more than 50 has been changed. Previously a root was computed by lifting but this showed to be unnecessarily expensive when for such degrees all roots can be computed in much less time. (V2.26-12)

  • A crash has been fixed in MaximalOrder when the Ramification parameter is specified and the number field is defined by a non-monic or non integral polynomial. (V2.26-12)

  • $p$-adic rings constructed as a completion of the integers or rationals will now have default precision given by the Precision parameter, consistent with completions of number fields. (V2.26-12)

Quadratic Fields

Bug Fixes:

  • IsQuadratic applied to an order of degree 2 which is not a radical extension has been fixed. (V2.26-11)

  • Non-exact division of elements is now possible in orders of degree 2 fields which are not radical extensions. (V2.26-11)

Algebraically Closed Fields

Bug Fixes:

  • A crash in the Roots function for polynomials defined over algebraically closed fields defined over function fields of small characteristic has been fixed.

  • A crash involving algebraically closed fields defined over a small finite field has been fixed.

Abelian Extensions of Number Fields

Bug Fixes:

  • A crash when computing the NumberField of a FldAb constructed using an invalid map has been improved to an error message. (V2.26-4)

Algebraic Function Fields

New Features:

  • The Localization of an order of a function field at an ideal of that order can now be computed. A valuation ring is returned.

Changes and Removals:

  • Series rings constructed as a completion of a rational function field will now have default precision given by the Precision parameter, consistent with completions of function fields. (V2.26-12)

  • The efficiency of the Montes algorithm as been improved in one place.

Bug Fixes:

  • A crash in NormEquation for function fields has been fixed. (V2.26-8)

  • A small improvement has been made to the prime choosing when computing Subfields of a prime characteristic algebraic function field represented as an extension of another algebraic function field (V2.26-9) and as an extension of a rational function field.

  • The embeddings between fields in a tower and the direct extension between 2 of these. (V2.26-10)

Galois Groups

Changes and Removals:

Bug Fixes:

  • A precision has been increased when computing GaloisGroups of polynomials over characteristic 0 rational function fields to improve the accuracy of results. (V2.26-7)

[]{#ssec:rfo_res_ring label="ssec:rfo_res_ring"}

Arithmetic Fields (Local)

$p$-adic Rings and their Extensions

New Features:

  • Exact $p$-adic rings and fields can be constructed and extended because of the inclusion of Christopher Doris' C package. These structures of type RngXPad and FldXPad were first documented in V2.26-6. Such structures and their elements can be approximated to as much precision as the objects they depend on allow, some to arbitrary precision. They are represented "lazily", knowing how they are computed but not being approximated unless necessary. In addition to some expected $p$-adic intrinsics, a RamificationPolygon and DiscriminantValuation can be computed for such exact extensions.

  • Elements of exact $p$-adic rings and fields (RngXPadElt, FldXPadElt) have some additional intrinsics which apply to them but not inexact elements. These intrinsics mitigate the infinite nature of the Valuation intrinsic for exact zeros. A WeakValuation can be obtained and valuation compared using ValuationEq and similar intrinsics where Eq is replaced by Ne, Ge, Gt, Le or Lt.

  • A specific type of polynomial ring over exact $p$-adic rings and fields is provided (RngUPolXPad) in addition to being able to construct the usual polynomial rings over these exact rings and fields. Polynomials can be converted to ExactPolynomials to which IsWeaklyZero and IsWeaklyEqual can be applied. The Factorization of exact polynomials can be computed as well as their Roots. Further to the construction of a NewtonPolygon, RamificationResidualPolynomials can be calculated.

Bug Fixes:

  • The printing of elements of precision 1 fields has been fixed so that the O() term uses the correct uniformizer name instead of 0. (V2.26-4)

  • The comment attached to SetPrecision has been adjusted to clarify that it is DefaultPrecisions which are changed rather than the actual precisions of a ring or field and its coefficient rings. (V2.26-5)

  • An improvement recently made to Factorization of polynomials has been fixed. (V2.26-5)

Series Rings

Bug Fixes:

  • Improvements have been made to the Factorization of inseparable polynomials over series rings and extensions of series rings. It is also now possible to take $p$-th power roots of elements of extensions of series rings of characteristic $p$. (V2.26-10)

Valuation Rings

New Features:

  • Valuation rings can now be constructed over algebraic number fields and function fields. These valuation rings have the same functionality as the existing valuation rings, including Euclidean operations on elements. Matrices can be constructed over these valuation rings and HermiteForms of these matrices can be computed.

Basic Rings and Fields

Integer Ring

New Features:

  • Parallel versions of the ECM and MPQS algorithms for integer factorisation are now available. These are selected by first calling SetNthreads(k); (to select $k$ threads) and optionally the StartWorkers procedure (to select worker nodes) before general integer factorisation is called. (The MPQS algorithm also no longer uses files to communicate between workers.)

Changes:

  • The command-line argument -q to Magma is no longer supported/needed, and the procedure MPQS(n, S) (where $S$ specified a directory to communicate between workers) has been removed, since the algorithm no longer uses files.

Real and Complex Fields

Bug Fixes:

  • A problem with printing polynomials over complex fields with imaginary numbers has been fixed.

  • An inaccuracy in root finding over complex fields arising from computing reduced modules of hyperelliptic curves has been fixed. (V2.26-7)

Univariate Polynomial Rings

Bug Fixes:

  • A hang in polynomial factorisation arising when testing isomorphism of hyperelliptic curves has been fixed. (V2.26-7)

Multivariate Polynomial Rings

Bug Fixes:

  • An incorrect result when computing $n$-th roots of recursively defined polynomials has been fixed.

Local Multivariate Polynomial Rings

Bug Fixes:

  • A crash in NormalForm(f, S) where $S$ is a set or sequence of local multivariate polynomials has been fixed.

Rational Function Fields

Changes:

  • The function Evaluate(f, e) for rational function field elements has been improved to avoid confusing automatic coercion of $e$. (V2.26-4)

Coding Theory

General Linear Codes

New Features:

  • The intrinsic StandardForm now works for codes defined over prime-powered residue rings, not just $\mathbb{Z}_4$.

Linear Codes over Finite Fields

Bug Fixes:

Commutative Algebra

Ideal Theory and Gröbner Bases

New Features:

  • The parallel version of the Faugere $F_4$ algorithm (selected by SetNthreads) has been greatly improved in the linear algebra phase, while the symbolic reduction and critical pair management phases have been parallelised for the first time. This includes the cases of ideals defined over $\mathrm{GF}(q)$ for $2<q<2^{30}$ where $q$ is not a power of 2 or over $\mathbb{Q}$. New record timings for a 4-core Intel Core i7-7700 CPU (3.60GHz) include the following (for computing the grevlex Gröbner basis in each case):

    • The Cyclic-9 roots ideal over GF(32003): 10.2 secs (4 cores) or 29.3 secs (1 core);

    • The Cyclic-10 roots ideal over GF(32003): 601.2 secs (4 cores) or 1957.1 secs (1 core).

    • The Cyclic-9 roots ideal over $\mathbb{Q}$: 144.3 secs (4 cores) or 286.1 secs (1 core), using 750MB for either computation;

    • The Cyclic-10 roots ideal over $\mathbb{Q}$: 5.2 hours (4 cores) or 16.1 hours (1 core), using 46GB for either computation.

  • The main strategy for the Faugere $F_4$ algorithm has been extended so that by default a limit on the number of critical pairs is now dynamically chosen for each new step (so the pairs limit varies throughout the algorithm). This leads to major speedups for computing Gröbner bases of many types of input ideal for which the previous default strategy of no pairs limit was not optimal; that previous default behaviour (with no pairs limit for each step) can now be selected by setting the parameter PairsLimit to 0.

  • The Faugere $F_4$ has been improved so that the setup of higher-degree critical pairs is delayed as much as possible. As a result, if the final Gröbner basis is trivial or has very small degree polynomials only, the critical pair management is often greatly sped up. The low-level subalgorithm for critical pairs management (used in both the Faugere $F_4$ and Buchberger algorithm) has also been significantly sped up itself in general.

  • The second pass reduction in the linear algebra phase of the Faugere $F_4$ algorithm (which sometimes can be quite expensive) has been significantly sped up.

  • The linear algebra phase of the Faugere $F_4$ algorithm has a new representation for computations over $\mathrm{GF}(p)$ for $p<256$. This yields signifcant memory savings when the Gröbner basis is large, together with a moderate speedup.

  • New function MinRankSystem(K, n, k, r) to create a multivariate polynomial system corresponding to a random instance of the square $(n,k,r)$-MinRank problem over a finite field $K$.

  • New function HFESystem(q, n, D) to create a multivariate polynomial system corresponding to a random instance of the Hidden Field Equations (HFE) system over $\mathrm{GF}(q)$ with $n$ variables and secret degree $D$.

  • The function MinimalBasis for an ideal of a multivariate polynomial ring has been improved in the search for a grading to make the input homogeneous if it is not already. The new function HomogeneousWeightsSearch also does the search for weights.

  • The general strategy for primary decomposition of positive-dimensional ideals has been improved.

Bug Fixes:

  • A crash in the symbolic phase of the $F_4$ algorithm in the sparse monomial case has been fixed. (V2.26-2)

  • A crash in the version of the $F_4$ algorithm that uses the sparse monomial representation when there are more than 255 variables has been fixed. (V2.26-7)

  • A bug in primary decomposition (arising from PrimeComponents applied to a scheme) has been fixed. (V2.26-5)

  • A crash in Dimension for ideals with a grading containing zeros has been fixed. (V2.26-7)

Affine Algebras

Bug Fixes:

  • The functions VectorSpace, Dimension, MatrixAlgebra and Algebra applied to an affine algebra $Q=I/J$ have been fixed to include the case where $I$ is a proper ideal. The same is now true for quotients of free algebras. (V2.26-7)

  • A crash in Image for homomorphisms between modules defined over affine algebras has been fixed. (V2.26-7)

Invariant Theory

Bug Fixes:

  • An bug causing an incorrect (non-minimal) result in FundamentalInvariants has been fixed. (V2.26-9)

  • A bug causing an occasional incorrect result when computing the relation ideal of an invariant ring has been fixed (V2.27-1).

Geometry

Convex Polytopes and Polyhedra

Bug Fixes:

  • A bug in InteriorPoints that could miss a point with one-dimensional polytopes having a rational endpoint and an integral endpoint was fixed (V2.27-1).

Groups

Classical Groups

New Features:

  • In recent years fast methods have been implemented for determining the conjugacy classes of elements in most classical matrix groups. In this version of Magma the coverage of fast conjugacy class construction has been extended to include the following types of group:-

    • Conformal classical groups.

    • The projective versions of the classical groups of these types:-\ $GL$, $SL$\ $Sp$\ $GU$, $SU$\ $GO+$, $SO+$, $Omega+$\ $GO-$, $SO-$, $Omega-$\ $GO$, $SO$, $Omega$.

  • The intrinsic ClassicalGroupType(G) and the algorithms which compute the conjugacy classes of a classical group are not restricted to the standard copies.

Databases of Groups

New Features:

  • The small groups database has been expanded to include all groups with order a product of at most 4 primes. This implements the catalogue of Dietrich, Eick and Pan.

Lattices and Quadratic Forms

Lattices

New Features:

  • An effective parallel version of close vector enumeration in lattices was completed. (V2.26-4)

  • The FP-based LLL algorithm has been parallelised (selected by SetNthreads) so that non-trivial speedups are achieved for lattices with medium dimension and large integer entries (occurring in several computations in number theory and in modular reconstruction algorithms).

  • New functions ShortVector, ShortestVector, CloseVector, ClosestVector to return a single non-zero short/close/shortest/closest vector in a lattice.

Bug Fixes:

  • A bug in CloseVectors where it would sometimes miss close vectors when the lattice basis had small entries and the input vector had very large entries has been fixed.

Linear Algebra and Module Theory

Matrices

New Features:

  • The algorithm for final saturation when computing the nullspace of a matrix over $\mathbb{Z}$ has been improved.

  • The algorithm for computing the nullspace of a large dense matrix over $\mathbb{Q}$ has been improved.

  • The general algorithm for saturation of an integral lattice has been improved.

Bug Fixes:

  • A bug in InvariantFactors for matrices over small finite fields has been fixed. (V2.26-9)

  • A bug where constructing random matrices over the finite field GF(2, 30) occasionally gave invalid entries has been fixed. (V2.26-11)

Sparse Matrices

New Features:

  • The function ChangeRing for sparse matrices now allows the map argument (as for dense matrices).

Bug Fixes:

  • The procedure SetEntry has been fixed to extend the matrix to the correct number of rows when the last argument is zero and the existing row is zero. (V2.26-10)

Linear Associative Algebras

Associative Algebras

Bug Fixes:

  • The error checking of the index to . has been improved. (V2.26-4)

Basic Algebras

Bug Fixes:

Matrix Algebras

Bug Fixes:

  • A crash in Centre for matrix algebras with large numbers of generators has been fixed. (V2.26-12)

Finitely Presented Associative Algebras

Bug Fixes:

  • A bug in reduction of the final Groebner basis computed for some types of ideal of a free algebra has been fixed. (V2.26-11)

Parallelism

New Features:

  • New procedure StartWorkers to start up Magma worker jobs remotely without having to start up Magma jobs on remote machines manually. This is useful for the internal distributed algorithms (such as code/lattice enumeration, integer factorisation). As a result, the -w command line option is no longer needed unless more manual control is desired. Note that the main magma driving script should be updated too.

Representation Theory

$K[G]$-Modules

New Features:

  • The computation of irreducible $G$-modules in characteristic zero for a pc-group $G$ has been made more stable.

  • The main algorithm for the computation of irreducible $G$-modules in characteristic zero has been improved, particularly in the case that the composition length of $G$ is non-trivial.

Bug Fixes:

  • A crash in AHom for trivial action has been fixed.

  • A slowdown when deleting large sequences of $G$-modules has been fixed.

  • A bug has been fixed in IrreducibleModules(G, RationalField()) for a PC group $G$, where isomorphic modules were returned.

  • A bug in DirectSumDecomposition for $G$-modules where $G$ was an unconditioned PC group has been fixed. (V2.26-10)

Modules over Algebras

Bug Fixes:

System

GPU support

Bug Fixes:

  • A crash in large matrix muliplication over GF(5) on V100 GPUs has been fixed. (V2.26-4)