xTras version 1.4.2

• Added RicciToRiemann.
• Added KretschmannToRiemann.
• ToRiemann also converts rank-2 curature tensors if the curvature relations are not enabled.
• ToRicci also converts contractions of Riemann tensors to Ricci tensors even if the curvature relations are not enabled.

xTras version 1.4.1

• IndexConfigurations gives correct results for expressions with more than one tangent bundle.
• EulerDensity is faster, and takes the option Verbose.
• xTras now needs xTensor 1.1.1.

xTras version 1.4.0

• AllContractions automatically parallelizes on Mathematica 8 or newer.
• AllContractions has an improved algorithm.
• AllContractions directly calls the external xPerm executable, which makes it about 5x faster.
• ConstantSymbolsOf now takes multiple arguments.
• RiemannSimplification's error-message is more human-readable.

xTras version 1.3.3

• xTras now requires xTensor 1.1.0.
• Products of symmetrized derivatives that commutate are now fully canonicalized.
• Improved speed of perturbations of symmetrized derivatives.
• Fixed two PrintAs related issues.
• FromIndexFree is now compatible with $AutoSymmetrizeCovDs = True.
• CollectTensors is more verbose while simplifying coefficients.

xTras version 1.3.2

• Symmetrized derivatives use the chain rule on scalar functions.
• Improved speed of SymmetrizeCovDs in some situations.
• SymmetrizeCovDs strips all dummy indices before caching.
• VarD on symmetrized derivatives w.r.t. to another derivative works.
• Symmetrized covariant derivatives pass Validate.
• CollectTensors is faster on expressions that are (partially) collected.
• TensorWrapper is much faster on large products (was exponential in the number of terms, is now linear).
• Fixed warning message in SolveTensors.

xTras version 1.3.1

• Added the function ConstantSymbolsOf.
• Added possibility (controlled by the variable $AutoSymmetrizeCovDs)
  to automatically symmetrize covariant derivatives.
• Added caching to SymmetrizeCovDs, controlled by the "UseCache" option.
• Improved algorithm for symmetrizing covariant derivatives in the case
  when there is no torsion and the derivative is metric-compatible.
• Perturbation no longer expands symmetrized covariant derivatives.

xTras version 1.3.0

Big changes:

• Added functions for symmetrizing covariant derivatives (SymmetrizeCovDs and ExpandSymCovDs).
• Added the symmetrized Riemann tensor.

Other changes:

• Added the function ToRiemann.
• RiemannYoungProject only projects if the Riemann tensor has its full symmetries; otherwise it does nothing.
• RiemannYoungProject also projects Weyl and symmetrized Riemann tensors.
• TableauSymmetric now inherits the value of its option ManifestSymmetry from YoungSymmetrize.

xTras version 1.2.3

This is a small point release, adding just one function:

• Added GradChristoffelToRiemann, which converts partial derivatives of Christoffel symbols to Riemann tensors.

xTras version 1.2.2

Again a small bugfix release:

• RemoveConstants, RemoveTensors, and TermsOf now also work on non-expanded sums.

xTras version 1.2.1

This is a small bugfix release. The changes are:

• Defining a metric with PD as its Levi-Civita derivative is no longer broken.
• Extra curvature tensors Schouten, SchoutenCC, and EinsteinCC tensors are defined only when there
  is curvature. Furthermore, they become non-symmetric when there is torsion, and are properly
  extended, projected, and orthogonalized when needed.
• Added torsion to the RHS of the contracted Bianchi identities returned by CurvatureRelationsBianchi.