Hi Ian,
Wrapping `sim.output_field_function` in a step function should do the trick
(leaving esq_mag in its original form).
```
def my_output(sim):
sim.output_field_function('E_sq', [mp.Ex, mp.Ey, mp.Ez], esq_mag)
sim.run(mp.to_appended('test', mp.at_every(0.1, my_output)), until=10)
```
`at_every` expects a function, but was getting the result of calling
`mp.output_field_function`, which returns 'None'.
I'll make some improvements to the documentation based on your helpful
suggestions.
Thanks,
Chris
On Wed, Feb 7, 2018 at 6:25 PM, Ian Sage <i...@sage.myzen.co.uk> wrote:
> The documentation is not all that clear about the procedure to follow,
> when using the Python interface. I'd like to call a function like:
>
> def esq_mag(r, ex, ey, ez):
> return ex*ex.conjugate()+ey*ey.conjugate()+ez*ez.conjugate()
>
> from the at_every construct - I initially used the above function together
> with:
>
> sim.run(mp.to_appended(prefix, mp.at_every(0.1,
> sim.output_field_function('E_sq', [mp.Ex, mp.Ey, mp.Ez], esq_mag))),
> until=t)
>
> but the program runs to the point where output is triggered, then stops
> with a lengthy error message, terminating:
>
> File "/usr/lib/python3.6/site-packages/meep/simulation.py", line
> 28, in get_num_args
> return func.__code__.co_argcount
> AttributeError: 'NoneType' object has no attribute '__code__'
>
> That does not surprise me as the docs state I have to pass a function to
> the sim.run function, not the result of evaluating a function. So I tried
> again, supplying in the spirit of the instructions related to Scheme "a
> function my-weird-output of no arguments that, when called, outputs our
> function f." So I constructed a function to do that:
>
> def esq_mag():
> def _esq_mag(r, ex, ey, ez):
> return ex*ex.conjugate()+ey*ey.conjugate()+ez*ez.conjugate()
> return _esq_mag
>
> but the result is another error:
>
> TypeError: esq_mag() takes 0 positional arguments but 4 were given
>
> OK - I need to handle those arguments to esq_mag, so
>
> def esq_mag(r, ex, ey, ez):
> def _esq_mag(r, ex, ey, ez):
> return ex*ex.conjugate()+ey*ey.conjugate()+ez*ez.conjugate()
> return _esq_mag
>
> but now the program fails with:
>
> TypeError: must be real number, not function
>
> The above exception was the direct cause of the following exception:
>
> SystemError: PyEval_EvalFrameEx returned a result with an error set
>
> I have tried several variations without success; please, what construct
> should I be using?
>
> Also, if I try to use output_real_field_function as described in the docs,
> I get the error:
>
> AttributeError: 'Simulation' object has no attribute
> 'output_real_field_function'
>
> I'll be very grateful for any help,
>
> Ian
>
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