Hi, and thanks as always for cdb.

How should I go about writng a propagator and taking its derivative? I tried

```
from cdb.sympy.calculus import *
diff($1/(\eta_{\mu\nu} x^{\mu}x^{\nu})$, $x^{\mu}$);
```

but that doesn't work. Any advice?

Thanks GPN

0 votes

Best answer

I now tried

```
from cdb.sympy.calculus import *
\partial{#}::PartialDerivative;
x^{\rho}::Depends(\partial{#});
diff($1/(\eta_{\mu\nu} x^{\mu}x^{\nu})$, $x^{\rho}$);
```

which gave the error message

```
File "/home/gpn/.config/cadabra_packages/cdb/sympy/calculus.py", line 20, in diff
dvars.append( sbtmp.to_sympy() )
RuntimeError: Dependencies on derivatives are not yet handled in the SymPy bridge
```

so I conclude this is not yet possible in cdb. If anyone has a better answer please let me know.

Thanks GPN