dials.scale: determine_Imids infinite loop

[rjgildea]

Under some circumstances it appears that the _determine_Imids() method in dials.scale can enter an infinite loop, eventually consuming all available memory before being killed:

dials/algorithms/scaling/combine_intensities.py

Lines 142 to 150 in a8710a8

	def _determine_Imids(self, raw_intensities):
	if not self.Imids:
	avg = flex.mean(raw_intensities)
	Imid = flex.max(raw_intensities) / 10.0
	Imid_list = [0, 1, avg, Imid]
	while Imid > avg:
	Imid /= 10.0
	Imid_list.append(Imid)
	self.Imids = Imid_list

This has been observed in autoprocessing at DLS.

[rjgildea]

Logging the content of Imid_list before it enters the while loop gives:
[0, 1, -0.08802942570001496, 4230.601644563469]
I.e. avg is less than zero, so no matter how many times we divide Imid by 10, it will always be greater than avg.

[rjgildea]

Note that this function is duplicated further down in the same file (for MultiDatasetIntensityCombiner) so any bug fix should probably be applied here too:

dials/algorithms/scaling/combine_intensities.py

Lines 334 to 342 in a8710a8

	def _determine_Imids(self, raw_intensities):
	if not self.Imids:
	avg = flex.mean(raw_intensities)
	Imid = flex.max(raw_intensities) / 10.0
	Imid_list = [0, 1, avg, Imid]
	while Imid > avg:
	Imid /= 10.0
	Imid_list.append(Imid)
	self.Imids = Imid_list