Hi James, thanks. I looked at random image 15 and after trying a bunch of stuff it indexes fine if I use indexing.method=fft3d. The default for stills processing is fft1d, so I find this super interesting. For what it's worth, I pretty much never process stills without a target cell. I generated ~30 random images using your script and indexed them, then I got the unit cells with "dials.show *refined*.json | grep cell". They were all about the same. So I re-indexed random image 15 using fft1d but I also specified known_symmetry.cell=50,60,70,90,90,90 and it indexed fine. So, either indexing.method=fft3d or known_symmetry.cell=50,60,70,90,90,90 is sufficient to index random image 15. Certainly for experimental data I would recommend using known_symmetry as the results are always better. However, I'd like to look deeper at fft1d vs fft3d at some point. Cc'ing dials-support. Thanks! -Aaron On Fri, Feb 2, 2018 at 1:35 PM, James Holton wrote:

While testing the new simTBX diffraction image simulator Aaron and I found that some rather beautiful-looking images still won't index. Subsequently, I followed up with mosflm, which does succeed in these cases, even without prior knowledge of the cell or space group.

I have now run this 1000 times, varying only the crystal orientation, and found 171 cases of dials.stills_process failing to index the simulated image whereas mosflm had no trouble, and 5 cases where mosflm failed and dials.stills_process succeeded. There were no overlapping cases where both programs failed.

I have tarballed up the relevant files here: http://bl831.als.lbl.gov/~jamesh/bugreports/dials_index_020218.tgz

The tarball contains a "runme.com" shell script for reproducing these results, and also the tst_nanoBragg_forindex.py jiffy for making a test image given a provided random-number seed. For example:

libtbx.python ./tst_nanoBragg_forindex.py random 15

will create a file called noiseimage_001.cbf that dials.stills_process cannot index (at least in my hands). For those of you who don't have mosflm installed, the tarball incluses a copy, and the "autoindex.com" script should run on any linux system.

Any ideas as to why there is this discrepancy? Feels like an opportunity for a non-trivial improvement.

Something to ponder over the weekend, I suppose. Note that I recently checked in a few bug fixes to simTBX, but this analysis is unaffected by them, so you shouldn't have to update your build to reproduce this.

Cheers,

-James Holton MAD Scientist

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