Vectors in xPand

[Mohammad-Hossein Abbassi]

Hi guys;

I'm wonder if it is anyway to define a general vector as matter field in xPand. I find that the only vector field that is defined there, is "u" with (1,0,0,0) components. But I want to perform xPand calculation on a general Vector field. Is there any way to do it in xPand?

Thanks
Mohammad

[Obinna Umeh]

Hi Mohammad,

Yes, it is possible to define a general vector in xPand.

 If what you want is a vector that includes a peculiar velocity when perturbed in say conformal Newtonain gauge, this is how you do it.

Use a different notation for the vector in the slot  for vector in DefMatterFields  say DefMatterFields[um, dum, h].

When you perturb um it will include its perturbation dum decomposed on the background hypersurface with the induced metric h

I attached a minimal example.

If you want a totally different kind of vector, then you have to use DefProjectedTensor to define the vector  and assign whatever rules you may want to it.

Cheers,

Obinna

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[Mohammad-Hossein Abbassi]

Perfect!
Thank you so much, Obinna. It works.

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