warnings in test_sdm

[wholmgren]

https://dev.azure.com/solararbiter/pvlib%20python/_build/results?buildId=4054&view=logs&j=fc432b8b-e2e3-594e-d8b1-15597b6c1d62&t=309866e1-2cf4-5f00-3d0a-999fc3a0f279&l=209

through

https://dev.azure.com/solararbiter/pvlib%20python/_build/results?buildId=4054&view=logs&j=fc432b8b-e2e3-594e-d8b1-15597b6c1d62&t=309866e1-2cf4-5f00-3d0a-999fc3a0f279&l=295

So almost 100 lines of warnings.

[cwhanse]

Not bugs per se, the algorithm handles non-convergence when looping through the IV curves by continuing, although the rattling and squeaks are audible. I'd prefer to keep that behavior and silencing divide by 0 and invalid (nan) value warnings in place, if that's OK.

[wholmgren]

No problem with the algorithm, just its rattles and squeaks. Does it need to emit its own more useful warnings?

[cwhanse]

It could, but the causes for non-convergence may not be easy to identify and state. The returned dict includes a Boolean array that is False for IV curves for which it didn't get parameters. It could warn that the array is non-empty, but that seems unnecessary to me.