I was recently asked about performing some General Relativity computations from a paper by Plamen Fiziev, posted in the arXiv in 2013. It crossed my mind that this question is also instrumental to illustrate how these General Relativity algebraic computations can be performed using the Physics package. The pdf and mw links at the end show the same contents but with the Sections expanded.
General Relativity using Computer Algebra
Problem: for the spacetime metric,
a) Compute the trace of
where is some function of the radial coordinate, is the Ricci tensor, is the covariant derivative operator and is the stressenergy tensor
b) Compute the components of the traceless part of of item a)
c) Compute an exact solution to the nonlinear system of differential equations conformed by the components of obtained in b)
Background: The equations of items a) and b) appear in a paper from February/2013, "Withholding Potentials, Absence of Ghosts and Relationship between Minimal Dilatonic Gravity and f(R) Theories", by Plamen Fiziev, a Maple user. These equations model a problem in the context of a BranseDicke theory with vanishing parameter The Brans–Dicke theory is in many respects similar to Einstein's theory, but the gravitational "constant" is not actually presumed to be constant  it can vary from place to place and with time  and the gravitational interaction is mediated by a scalar field. Both Brans–Dicke's and Einstein's theory of general relativity are generally held to be in agreement with observation.
The computations below aim at illustrating how this type of computation can be performed using computer algebra, and so they focus only on the algebraic aspects, not the physical interpretation of the results.

GeneralRelativit.pdf GeneralRelativity.mw
Edgardo S. ChebTerrab
Physics, Differential Equations and Mathematical Functions, Maplesoft
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