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PerturbBackground

PerturbBackground[expr]
returns an (unexpanded) first order perturbation of expr on an arbitrary background.
PerturbBackground[expr, n]
returns an (unexpanded) nth order perturbation of expr on an arbitrary background.
  • The expansion parameter nor the the overall factor are not included in the result.
  • Tensors inside Perturbation heads are not replaced by their background values.
  • The following options can be given:
BackgroundSolution{}a list of replacement rules that send curvature tensors to their background values
ExtraRules{}a list of replacement rules for other tensors