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  • $\begingroup$ Is there are way to use this package to perform the calculation without specifying the variables that will be replaced a priori, simply to replace repeated variables? For example it seems like it would be unwieldy to specify the variables when used on the longer input I posted. Alternatively, I could just apply march's code commented under the OP to get a common set of variables and then use this package if what I'm asking isn't possible. $\endgroup$ Commented Feb 27, 2017 at 22:22
  • $\begingroup$ I'm a little confused what you're asking. All I've done in this example is write out your expression in the syntax expected by xAct. I haven't told it which dummy indices to rename, it figures that out on its own. (The DefManifold statement is just saying that the indices listed belong to a manifold which I've called M; you need to define a manifold before you can define tensors on it). The code may make more sense if you read a bit of the xTensor manual. It does require you to be a bit more methodical, and define things like manifolds and tensors in advance. $\endgroup$ Commented Feb 27, 2017 at 22:54