Skip to main content.


23 August 2015: Version 1.1.2 of xAct released:
  • New package SpinFrames, by T. Bäckdahl and S. Aksteiner, for the Newman-Penrose (NP) and Geroch-Held-Penrose (GHP) form of spinor equations.
  • Better support for the CTensor framework in xTerior.
  • Various improvements in TexAct.
  • LieDToCovD now handles connections with torsion.


15 February 2014: Version 1.1.0 of xAct released:
(Very many thanks to Alfonso García-Parrado, who was fully in charge of this release.)
  • New package xTerior, by A. García-Parrado and L. C. Stein, for exterior calculus.
  • Optimized Windows binaries of xperm.c prepared by T. Bäckdahl.
  • More functionality for tensors by components in xCoba.
  • Improved functionality in TexAct by T. Bäckdahl.
  • Improved functionality in xTras by T. Nutma.
  • There is a new page for development of new packages in xAct, mantained by L. C. Stein and and T. Nutma.


27 January 2013: Version 1.0.5 of xAct released:
(Thanks to Teake Nutma and Cyril Pitrou for much help with this release!)
  • xAct is now compatible with Mathematica 9.
  • New package xPand, by C. Pitrou, X. Roy and O. Umeh, for cosmological perturbation theory around homogeneous spacetimes.
  • The xTras package is now included in the xAct distribution.
  • Functions Permute and PowerPermute respectively renamed PermProduct and PermPower in xPerm.
  • Improved some basic functionality in the area of induced metrics in xTensor.
  • Started new notation for tensors by components in xCoba.


5 May 2012: Version 1.0.4 of xAct released:
(Thanks to Thomas Bäckdahl for much help with this release!)
  • Yet another bug-fix version.
  • Package TexAct excised from xTensor and SymManipulator to handle conversion to Tex output.
  • Package AVF now included in the xAct distribution.
  • Added command xTension to provide hooks to modify the action of the Def/Undef commands.
  • The SymManipulator package can now do irreducible decompositions of spinor expressions.
  • Added partial support for SeriesData expressions (everything but ToCanonical).


25 October 2011: Version 1.0.3 of xAct released:
  • This is another bug-fix version.
  • Updated Spinors for publication.
  • Added messages reporting non-standard configuration in some packages.
15 July 2011: Version 1.0.2 of xAct released:
  • This is mainly a bug-fix version.
  • Release of the first public version of SymManipulator, a package contributed by T. Bäckdahl to handle symmetrized tensors.
  • Option FormatBasis for DefBasis and DefChart in xCoba to help in the formatting of all vectors/covectors of a basis.
17 April 2011: Version 1.0.1 of xAct released:
  • xAct is now compatible with Mathematica 8.
  • Various bug fixes and extensions. See the respective .History files.
  • Added support for conformal transformation using the option ConformalTo of DefMetric.
  • Improved commands TexPrint and TexBreak using code provided by T. Bäckdahl and B. Wardell.


30 September 2010: Versions 1.0.0 of xTensor and Spinors released:
  • Added new commands TensorD/TensorDerivative for alternative treatment of derivatives. See the example notebook TensorDerivative.nb.
  • Added new form of delta, the "superdelta", with groups of indices of arbitrary symmetry. Added a symmetrizer Sym head.
  • Tensors with non-atomic heads are now allowed.
  • Improved treatment of "frozen" (non-first) metrics.
  • Many small improvements and fixes. See xTensor.History for full details.
  • The main xAct webpage is now
10 January 2010: Version 0.9.9 of xAct rereleased with more bug fixes.


24 November 2009: Version 0.9.9 of xAct rereleased with some bug fixes.
9 September 2009: Version 0.9.9 of xAct released, on the same day of the celebration honoring the 65th birthday of Prof. Jesús Martín. This version of xAct will be nicknamed "Chus" after him.
  • Note that now the xAct.tar.gz bundle contains all packages.
  • Documentation of Spinors enlarged and rearranged.
  • xCoba has a command MetricCompute to construct sequentially components of curvature tensors. See file KerrNewmanExamples.nb.
  • Added Leibnitz operator, following Jan's suggestion.
  • Support for LaTeX printing of tensor expressions, with commands Tex, TexPrint and TexBreak.
  • Safer code for NoScalar.
  • Fixed some problems with VarD.


1 December 2008: Version 0.9.1 of Spinors released.
  • Added command IrreducibleDecomposition decomposing spinors in their symmetric-tracefree parts.
  • The package now handles spacetimes with torsion.
23 November 2008: Version 0.9.8 of xAct released.
Transition version with many small improvements in xTensor:
  • Better treatment of 1-dimensional spaces.
  • New functions for ADM-like decompositions: commands GaussCodazzi, ToInducedDerivative and DirCovDToLieD.
  • Fixed a number of problems with variational derivatives.
  • New command Cyclize, similar to Symmetrize, etc.
  • Faster manipulations of products of delta's.
  • Added option Method in ToCanonical, to choose how to deal with metric-incompatible derivatives.
11 August 2008: Spinors released.
Requires updating xAct to 0.9.7.
  • There is a full new package, Spinors, developed in collaboration with Alfonso García-Parrado, for computations with spinors on four-dimensional Lorentzian manifolds, including spinor-tensor translations. The doc file SpinorsDoc includes as examples the full Newman-Penrose and Geroch-Held-Penrose formalisms, developed from scratch there. Package released with version number 0.9.0. Please send us feedback.
  • Motivated by the use of an antisymmetric metric in Spinors, the treatment of symmetries of the delta and Basis tensors has been modified. Now they have the symmetries of the corresponding metric, or no symmetry if there is no metric available. This does not affect the standard case with a symmetric metric.
30 June 2008: Version 0.9.6 of xAct released
Version required by update of xPert.
  • xPert rewritten and much improved. Version 1.0.0 for publication.
  • xTensor updated to version 0.9.6. Introduced commands Implode and Explode to transform between derivatives of tensors and tensors, and viceversa.
  • xCoba updated to version 0.6.4. Treatment of determinants fully reorganized, now without absolute values, to handle complex changes of bases, like in Newman-Penrose calculus. New commands RuleToSet and SetToRule.
  • xCore has now a documentation file.
16 May 2008: Version 0.9.5 of xAct released
  • xTensor has lots of small improvements. Now there are variational derivatives and more powerful versions of IndexCoefficient and IndexCollect. Metric-compatible connections with torsion. Much internal cleaning. Unique ultraindices have been removed.
  • Created Google group for discussion on the xAct packages. Please register (see left panel in this page) and report bugs and comments using it.
  • I have been invited to spend 6 weeks this summer at Wolfram Research Inc. as "visiting scholar". Please, help to improve xAct before I get there on July 22nd.
5 March 2008: Version 1.0 of xPerm released
Version for publication!
  • The option MathLink has been transferred from xTensor to xPerm. In particular, it is now an option of CanonicalPerm instead of an option of ToCanonical. xTensor updated to 0.9.4 and Invar updated to 2.0.2 for compatibility.
8 February 2008: Version 2.0 of Invar released
Major update of the system:
  • Now Invar also handles differential invariants up to 12 derivatives of the metric and dual invariants up to 8 derivatives of the metric.
  • The new database contains more than 600 000 equations


6 November 2007: Version 0.9.3 of xAct released
Transition version:
  • The executable xperm has been finally compiled under Windows using cygwin. Only for Mathematica 6.
  • Reference Guide for xTensor completed, as well as the individual help pages for its 332 reserved words.
  • Function TraceDummy introduced. Highly efficient, but still under testing.
  • Further analyses and checks of compatibility between xAct and Mathematica 6. See the summary page.
15 August 2007: Version 0.9.2 of xAct released
This is a major update of the system:
  • Package xCore created.
  • xPerm now efficiently handles component indices and several vbundles simultaneously.
  • xTensor has several new functions: IndicesOf, SeparateMetric, SplitIndex and others. Extended concept of InertHead. Cut and paste now possible!
  • xCoba has many new capabilities, including full implementation of symmetries in the manipulation of components, new algorithms for efficient storage, new representation of component indices (allowing any integer), ...
  • More than 300 pages of documentation.
  • Full compatibility with Mathematica 6.0, and still with all 5.* versions.
  • There is a new webpage!