Set up a coordinate system to work with - the first one to be set is automatically taken as the differentiation variables for d_, the covariant derivative D_ and the dAlembertian
When Physics is initialized, the default spacetime metric is of Minkowski type. You can see the metric by querying Setup, as in Setup(metric);, or by directly entering the metric g_ with no indices
Check the nonzero components of Christoffel: because the default spacetime is of Minkowski type, there are none
Hence
Consequently, all the general relativity tensors defined in terms of Christoffel and derivatives of the metric g_ are also automatically zero
For the same reason the covariant derivative ; for illustration purposes Define an arbitrary spacetime tensor
To set the scenario to be an arbitrary non-galilean spacetime, set the metric to be arbitrary (that is, depending on 10 arbitrary functions of the spacetime coordinates )
When the indices are not numerical, Christoffel returns itself after normalizing its second and third indices taking advantage of the symmetry under exchange of them
To express Christoffel in terms of its definition in terms of the spacetime metric g_, use convert to g_
To rewrite expressions like this one back in terms of Christoffel and its derivatives use convert(... Christoffel)
Related to displaying the components of Christoffel, it is convenient to have a compact display of the 10 arbitrary functions entering the metric as well as of their derivatives; for that purpose use the enhanced display scheme of the differential equation packages.
So from herein, in the display of expressions, derivatives are displayed as indexed and the functionality of the arbitrary functions is suppressed.
Check the value of for = = = 1
Now of for = = = 1 (note you enter the contravariant index prefixed by ~)
To compute with a representation for Christoffel without actually performing the operation, use the inert form %Christoffel. To afterwards perform the operation use value
Compute Arrays with all the components of and
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Because these arrays of values are computed by already taking into account the character (covariant/contravariant) of each index, you do not need to indicate furthermore that character. Thus, this is the all covariant with = = = 1
and this is the value of for = = = 1
Compare with the output of in eq (27)
The Schwarzschild metric in spherical coordinates (see g_) and the four 2 x 2 matrices for by giving values to its first index