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xTras package
xTras is a field-theory inspired add-on package for xAct. It contains new functions for doing tensor algebra, making Ansatze, computing contractions, and much more.

Below is a list of new functionality in xTras. If you're new to xAct, have a look at the introduction to xAct.
Basic functions
MapTimed timed version of Map
MapTensors map over tensors

Combinatorics
AllContractions gives all contractions of an expression
MakeTraceless makes an expression traceless
ConstructDDIs constructs dimensionally dependent identities

Tensor algebra
CollectTensors collects all tensorial terms
CollectConstants collects all constant symbols
SolveConstants solves equations with respect to constant symbols
SolveTensors solves equations with respect to tensors

Symmetrized covariant derivatives
SymmetrizeCovDs symmetrizes covariant derivatives
ExpandSymCovDs expands symmetric covariant derivatives
SymCovDQ sets covariant derivatives to be symmetrizable

Young tableaux
YoungProject projects tensors onto a Young tableau
RiemannYoungProject projects Riemann tensors onto their Young tableau
TableauSymmetric generates the SGS of a Young tableau

Simplification
FullSimplification simplifies curvature tensors as much as possible
SortCovDsToDiv automatically sorts covariant derivatives to divergences
SortCovDsToBox automatically sorts covariant derivatives to boxes

Curvature tensors
SymRiemann the symmetrized Riemann tensor
Schouten the Schouten tensor
SchoutenCC the cosmological Schouten tensor
EinsteinCC the cosmological Einstein tensor
ToRicci converts curvature tensors to Ricci tensors where possible
ToRiemann converts curvature tensors to Riemann tensors where possible

Killing vectors
KillingVectorOf defines a Killing vector

Pseudo index-free notation
IndexFree head for pseudo index-free expressions
ToIndexFree converts to pseudo index-free
FromIndexFree converts from pseudo index-free

Perturbations on (A)dS and flat backgrounds
SymmetricSpaceRules rules for (A)dS backgrounds
ExpandBackground perturb and expand on generic backgrounds
ExpandFlat perturb and expand on flat backgrounds

Invariants of Riemann tensors
EulerDensity gives the Euler density
ProductInvariants gives a basis for invariants of Riemann tensors

xCoba extensions
ComputeBasisValues computes values of basis elements
ImplodedTensorValues computes values of derivatives of tensors
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