Greetings all - My interest in the rest of the discussion of experimental precision and error notwithstanding, and at the risk of stating explicitly what some might consider obvious, it seems to me that no one has actually (intentionally) asserted that they have determined the unit cell to 10^-20 meter precision. Rather, I find it far more likely that some program just output the floating point representation of a 3-decimal-place number without a proper 3-decimal-place format string (something like `printf(“%f”, _cell.length_a)` instead of `printf(“%5.3f”, _cell.length_a)`, perhaps). The extra digits are the “noise” of floating point rounding error. Notice the repeating 9’s and 0’s after 3 decimal places in each of the values in question:
_cell.entry_id 4c69 _cell.length_a 100.152000427 ==> 100.152 _cell.length_b 58.3689994812 ==> 58.369 _cell.length_c 66.5449981689 ==> 66.545 _cell.angle_alpha 90.0 _cell.angle_beta 99.2519989014 ==> 99.252 _cell.angle_gamma 90.0 Each of these “extra precise” numbers should simply have been output with only 3 decimal places. But I suppose this still doesn’t answer the original question of *which* program actually needs to be fixed. Cheers, Jared -- Jared Sampson Xiangpeng Kong Lab NYU Langone Medical Center http://kong.med.nyu.edu/ On Jul 23, 2014, at 5:44 PM, Bernhard Rupp <hofkristall...@gmail.com<mailto:hofkristall...@gmail.com>> wrote: The representation is simply non-parsimonious. There is no meaning to the zepto-meter digits. Numquam ponenda est pluralitas sine necessitate. BR From: James Holton [mailto:jmhol...@lbl.gov] Sent: Wednesday, July 23, 2014 9:58 PM To: b...@hofkristallamt.org<mailto:b...@hofkristallamt.org>; CCP4BB@JISCMAIL.AC.UK<mailto:CCP4BB@JISCMAIL.AC.UK> Subject: Re: [ccp4bb] Protein Crystallography challenges Standard Model precision Where is it written that compactness of representation and accuracy/precision are the same thing? Is 1/3 more or less precise than 0.333 ? If mmCIF were a binary floating-point format file, there would be more "decimal places" in the precision of the stored value for the unit cell, despite fitting into only 4 bytes instead of the 13 bytes of text some seem offended to see below. Would that be better? Or worse? -James Holton MAD Scientist On 7/22/2014 4:01 AM, Bernhard Rupp wrote: I am just morbidly curious what program(s) deliver/mutilate/divine these cell constants in recent cif files: data_r4c69sf # _audit.revision_id 1_0 _audit.creation_date ? _audit.update_record 'Initial release' # _cell.entry_id 4c69 _cell.length_a 100.152000427 _cell.length_b 58.3689994812 _cell.length_c 66.5449981689 _cell.angle_alpha 90.0 _cell.angle_beta 99.2519989014 _cell.angle_gamma 90.0 # Maybe a little plausibility check during cif generation might be ok Best, BR PS: btw, 10^-20 meters (10^5 time smaller than a proton) in fact seriously challenges the Standard Model limits.. ---------------------------------------------------------------------------- ------------ Bernhard Rupp k.-k. Hofkristallamt Crystallographiae Vindicis Militum Ordo b...@ruppweb.org<mailto:b...@ruppweb.org> b...@hofkristallamt.org http://www.ruppweb.org/ ----------------------------------------------------------------------- ------------------------------------------------------------ This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain information that is proprietary, confidential, and exempt from disclosure under applicable law. Any unauthorized review, use, disclosure, or distribution is prohibited. If you have received this email in error please notify the sender by return email and delete the original message. Please note, the recipient should check this email and any attachments for the presence of viruses. The organization accepts no liability for any damage caused by any virus transmitted by this email. =================================
