I am studying the software by

https://cadabra.science/notebooks/schwarzschild.html

and I am redoing the steps present in Chapter 6, on the Schwarchield coordinates. When I'm going to calculate the inverse metric, using the complete algorithm:

```
{r,t,\phi,\theta}::Coordinate;
{\mu,\nu,\rho,\sigma,\lambda,\kappa,\chi,\gamma,\alpha,\beta#}::Indices(values= t,r,\phi,\theta},position=independent);
\partial{#}::PartialDerivative;
g_{\mu\nu}::Metric;
g^{\mu\nu}::InverseMetric;
# Schwarchield metric:
scw:= { g_{t t} = -(1-2 M/r), g_{r r} = 1/(1-2 M/r), g_{\theta\theta} = r**2, g_{\phi\phi}=r**2 sin(\theta)**2 };
# inverse metric:
complete(scw, $g^{\mu\nu}$);
```

the following error:

```
NonInvertibleMatrixError: Matrix det == 0; not invertible.
At:
/usr/lib/python3/dist-packages/sympy/matrices/matrices.py(3587): inverse_GE
/usr/lib/python3/dist-packages/sympy/matrices/dence.py(265): _eval_inverse
/usr/lib/python3/dist-packages/sympy/matrices/matrices.py(3672): inv
<\string>(1): <\module>
/usr/lib/python3/dist-packages/sympy/parsing/sympy_parser.py(902): eval_expr
/usr/lib/python3/dist-packages/sympy/parsing/sympy_parser.py(1008): parse_expr
<\string>(2): <\module>
```

Would anyone know if there is a problem with sympy?Because I’ve updated several times.