1 | initial version |

Unfortunately, the built-in function `spherical_harmonic()`

has many issues, as explained in this post (see also ticket #25034).

As suggested in the above post, a workaround is to use the function `spin_weighted_spherical_harmonic()`

of the SageMath package kerrgeodesic_gw with a zero weight, so that you get the standard spherical harmonics. A limitation is that this works only for specific values of $(l, m)$, i.e. you cannot keep $l$ and $m$ as symbolic variables.
See here for the documentation and examples of use of `spin_weighted_spherical_harmonic()`

.
Installing kerrgeodesic_gw in SageMath is easy: open a terminal and run

```
sage -pip install kerrgeodesic_gw
```

NB: on CoCalc, you have to add the option `--user`

:

```
sage -pip install --user kerrgeodesic_gw
```

2 | No.2 Revision |

Unfortunately, the built-in function `spherical_harmonic()`

has many issues, as ~~explained ~~discussed in this post (see also ticket #25034).

As suggested in the above post, a workaround is to use the function `spin_weighted_spherical_harmonic()`

of the SageMath package kerrgeodesic_gw with a zero weight, so that you get the standard spherical harmonics. A limitation is that this works only for specific values of $(l, m)$, i.e. you cannot keep $l$ and $m$ as symbolic variables.
See here for the documentation and examples of use of `spin_weighted_spherical_harmonic()`

.
Installing kerrgeodesic_gw in SageMath is easy: open a terminal and run

```
sage -pip install kerrgeodesic_gw
```

NB: on CoCalc, you have to add the option `--user`

:

```
sage -pip install --user kerrgeodesic_gw
```

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