I think you can do away with the comments here if you just define

```
LARGE_VALUE = 1.0e6
```

If you do this in the Cython file, you can reuse it when initializing `u_out` in `_eikonal`. You might also want to define a `SMALL_VALUE` so that you don't have random numbers popping up in the code. (Do you need both `1.0e-6` and `1.0e-20`? Is there a reason other than the fact that another implementation used these values?)