February 2009 - Cosmo-torun

some notes after today's talk - LDM
by Boud Roukema 22 May '09

22 May '09

witam cosmo-torun * circular polarisation from synchrotron processes? Kennett & Melrose, 1998, PASA, 15, 211 http://www.atnf.csiro.au/pasa/15_2/kennett/paper/node3.html > In some sources it may be that the relativistic > particles are electron-positron pairs (e.g., Wilson & > Weiler 1997). Electrons and positrons contribute with > the same sign to the linearly polarized component and > with the opposite sign to the circularly polarized > component. If the distributions of electrons and > positrons are the same the wave modes can have no > circular component and, more importantly, the intrinsic > circular polarization from the synchrotron radiation > sums to zero. So if we have different distributions of electrons and positrons, then we get a circular polarisation component. i'm sure there must be more basic texts on this subject... pozdr boud

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cosmo workshop wt 14:00 20.01.09 B Lew: 'A high significance foreground non-Gaussian signal ?'
by Boud Roukema 25 Feb '09

25 Feb '09

witam, Cosmo workshop tomorrow wtorek 20.01.09 at 14:00 @KRA. Bartek Lew will talk about his present project: 'A high significance foreground non-Gaussian signal ?' Everyone is welcome, but be warned: this is a research level work session, most likely in English. pozdr boud

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200-bit precision floating point arithmetic and trigonometry?
by Boud Roukema 03 Feb '09

03 Feb '09

hi cosmo-torun, This follows from a conversation some of us had recently. Debian stable (etch) includes GMP and MPFR - i ran a test program which quite nicely does e.g. 200-bit floating point operations, including trig functions, and gets reasonable answers. :) Source + doc: http://gmplib.org/ http://www.mpfr.org/ These are both under the LGPL instead of the GPL, so it turns out that... the non-free program Mathematica uses the free program GMP ! So apparently non-free software libraries are not good enough for Mathematica for this purpose. Or Mathematica is just "abusing the commons". [the commons: http://en.wikipedia.org/wiki/The_commons ] pozdr boud On Wed, 14 Jan 2009, Bartosz Lew wrote: >>> But within standard types long double is better than double etc. >> >> i assume this means you've experimented with this? Based on the >> wikipedia entries, i suggested to Zbyszek that this could be >> interesting, but i haven't tried it. My understanding is that it >> pushes to the limit of the machine you're using, which can be better >> than 64bit, but is nowhere near 128bit. :) > > mmm, don't remember which means that probably not much. > > But, I never experienced a need for such extremely super-duper high accuracy. > As far as the calculation is actually correct within the given precision it's cool. > Eg. CMBFast works in 4byte float numbers and it's sufficient. > AFAIK people still very often use 4byte floats. > My opinion is that is the code returns wrong numbers its an indication that it should be rewritten > in smarter way rather than going to long doubles or quadruple precisions. > >> >> Tomorrow Thursday i've got linux@IF so i'm very unlikely to be at >> KRA. But that's not an argument against both of you coming here and >> doing stuff. :) > > ok. > > B. >

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