Error when tracking ParameterBeam through segment that is on CPU?

[jank324]

I found this in the ParameterBeam part of the Element.__call__ function:

if self.device != "cpu":
    raise DeviceError

I think this doesn't make any sense (though I'm not sure). We should look into this at some point.

[jank324]

Also ... this is checked after the actual calculations, which would have thrown an error about device mismatches already. We should really fix this!

[cr-xu]

I think initially the reasoning was that it doesn't make sense to shift the ParameterBeam to GPU, because the overhead would be more time-consuming than the actual tracking. But yes, it shouldn't really through an error now, I'll just fix this.