ENH: allow user to specify the scaling of singlediode ivcurve-pnts or a specify an array, series, or sequence

[mikofski]

This idea also came up somewhere in #409 or #410. Currently the singlediode ivcurve_pnts takes the following according to docstring:

ivcurve_pnts : None or int, default None
    Number of points in the desired IV curve. If None or 0, no
    IV curves will be produced.

idea 1:

In addition let the user specify a sequence. Should it be sorted? Which values do they correspond to, I, V or Vd? IMO we should sort and scale them to the max value, and then multiply by Voc to keep them in the 1st quadrant.

idea 2:

Add another argument like ivcurve_scale which could be 'log' or 'linear' or other? IMO the default should be a log scale

Other ideas? Yea or Nay?

[cwhanse]

Idea 1 - use keyword arguments maybe. V is most commonly used, I believe.

Idea 2 - I'm ok with this as an optional argument. I'd default to log (natural log) of V.

[adriesse]

I would suggest providing any options you can think of since this is kind of a do-it-all function. Maybe even accept a list of V or I values (fractions of Voc and Isc).

[wholmgren]

I think @adriesse makes a good point.

I also think we'd be better off in the long run if we moved this functionality from singlediode to a dedicated function. Maybe rename singlediode to singlediode_5points and make a new singlediode_curve function.

[cwhanse]

I'm working on this issue and would appreciate any reactions to this addition of a kwarg voltage in pvsystem.singlediode.

[mikofski]

I would be slightly more in favor of reusing ivcurve_pnts as voltages if a sequence is specified, instead of ignoring it if voltages is specified in as well. IMO this might lead to confusion or at least make it prone to oversight errors. I believe having a single keyword that dispatches differently based on duck-typing makes oversight errors less likely, because the intent is more closely matched to the type, ie: a sequence could really only mean voltages.

try:
    voltages = iter(ivcurve_pnts):
except TypeError:
    voltages = None
else:
    ivcurve_pnts = None

This works for all combinations:

ivcurve_pnts = None  # -> voltages=None, ivcurve_pnts=None
ivcurve_pnts = 123  # -> voltages=None, ivcurve_pnts=123 (also works if x=0)
ivcurve_pnts = [1, 2, 3]  # -> voltages=<list_iterator>, ivcurve_pnts=None
ivcurve_pnts = range(100)  # voltages=<range_iterator>, ivcurve_pnts=None 

then either iterate over voltages or if needed call list(voltages) or tuple(voltages) to expand the sequence