Make MALA allow repeated ask()

[MichaelClerx]

See #996

There's no reason not!

Also cleaned up the tests a bit

[codecov[bot]]

Codecov Report

Merging #994 (c211e33) into master (a6a1a39) will not change coverage. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##            master      #994     +/-   ##
===========================================
  Coverage   100.00%   100.00%             
===========================================
  Files           84        63     -21     
  Lines         8823      6277   -2546     
===========================================
- Hits          8823      6277   -2546     

Impacted Files	Coverage Δ
pints/_mcmc/_mala.py	100.00% <100.00%> (ø)
pints/io.py	100.00% <0.00%> (ø)
pints/_core.py	100.00% <0.00%> (ø)
pints/_util.py	100.00% <0.00%> (ø)
pints/noise.py	100.00% <0.00%> (ø)
pints/_logger.py	100.00% <0.00%> (ø)
pints/_log_pdfs.py	100.00% <0.00%> (ø)
pints/toy/_cone.py	100.00% <0.00%> (ø)
pints/_boundaries.py	100.00% <0.00%> (ø)
pints/_evaluation.py	100.00% <0.00%> (ø)
... and 77 more

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[ben18785]

Cool. Not sure about this one currently, to be honest. Let me think about it...

On Wed, Oct 9, 2019 at 12:17 AM Michael Clerx [email protected] wrote:

@MichaelClerx commented on this pull request.

In pints/_mcmc/_mala.py https://github.com/pints-team/pints/pull/994#discussion_r332773584:

•    if not self._ready_for_tell:
  

•    if self._proposed is None:
         raise RuntimeError('Tell called before proposal was set.')
  

•    self._ready_for_tell = False
  

It's more in line with what we have in the other MCMC methods, with the exception of the ones that do more complicated stuff in ask() than just set a proposal.

So no very strong reason! Just that it's possible to let users ask() as often as they like in this case (and always get the same result), and it lets us remove a variable...

We might want to disallow this everywhere instead though? In which case we'd have to update the documentation for SingleChainMCMC and MultiChainMCMC a bit to make this explicit...

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[MichaelClerx]

Made a ticket here #996

[MichaelClerx]

Can we re-open discussion on this, @ben18785 and @martinjrobins ? See especially https://github.com/pints-team/pints/issues/996

[MichaelClerx]

No thoughts on this? It needs to be resolve one of two ways, I think:

1. Make it so that you can only ask once, in every method: a second call to ask() breaks everything
2. Make it so that you can ask as often as you like, in every method.