On Friday, January 10, 2014 10:56:03 PM UTC+1, Comer wrote:
>
> Today I have been looking at the sympy tensor package. I have attached a
> script in which I am trying to end of defining the Einstein tensor: R_{a b}
> - 1/2 *g_{a b} * R. But the script does not succeed on the last step of
> evaluating the above expression and hence fails to agree to create the
> Einstein tensor. I am wondering what I am doing incorrectly?
>
> Thanks for advice.
>
> Comer
>
This is a bug, d0 and -d0 have not been recognized as dummy indices and are
not contracted. I think I'll have a look tomorrow.
In the meantime, you can use this workaround, replace it into your last
line:
gR = tensor_mul(Rational(1,2)*g(-a,-b) * R)
gR = TensMul(*gR.args)
Ric(a,-b) - gR
This basically forces reconstruction of the tensor, and the dummy index
gets recognized this time.
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