Nice Scott
On Mon, Nov 23, 2009 at 1:07 PM, Ed Pozharski <epozh...@umaryland.edu>wrote: > Ian, > > On Mon, 2009-11-23 at 17:34 +0000, Ian Tickle wrote: > > Ed, > > > > > For instance, if angles are measured in degrees and x<<1 > > > sin x ~ pi * x / 180 > > > sin x ~ x > > > > Your equations cannot simultaneously be true & in fact the 1st one is > > obviously wrong, the 2nd is right. In the 1st case I think you meant > > (substituting 'x*deg' for 'x' in your correct 2nd equation): > > > > Hmm... It's not the same x in these two equations - one is measured in > degrees, the other in radians. > > > Just one: it's a<=b<=c. In any case, this comment is analogous to Henry > > Ford's famous sales pitch for the Model T: "You can have a car in any > > colour so long as it's black". Tell me, which would you say makes more > > sense: a) 1 person spends 10 secs adding 10 lines to the syminfo file > > once and for all, or b) many people post queries to CCP4BB about > > re-indexing their MTZ files because the processing mis-identified 2-fold > > screw axes from the systematic absences? > > > > Tough call. On one hand, refusing P22121's right to exist is > discrimination, on the other - these are the subtleties that help > understanding so this has some educational value. Then there is > Ockham's razor (which I personally believe people sometimes take too > far). I think you pose the question in the way which pushes towards > certain answer, let me try it differently: > > Which one makes more sense: > 1) people learning more about space groups and reading the manuals of > the software they are using to process data or > 2) adding more space groups and using more paper to print the > International Tables for Crystallography (gently hugs an imaginary > tree)? > > Seriously though, I think it makes sense to keep just P21212, because > you don't get a different crystal form by axes permutation. > > > > PS. By the way, did you notice that pi^2 ~ g ? I > > > > ... and did you notice that e^(i*pi) + 1 = 0 connects the 5 fundamental > > mathematical constants? - that also has nothing whatsoever to do with > > this thread ;-). > > > > Oh yeah - e^(i*pi)=-1 is my favorite meditation object :-) Nicely > connects arithmetics, geometry, calculus and complex analysis. > > Cheers, > > Ed. > > -- > -- Scott D. Pegan, Ph.D. Assistant Professor Chemistry & Biochemistry University of Denver
