Nic, Thanks,it will take a while (as usual) to implement. Bob R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814
-----Original Message----- From: Nicolae Popa [mailto:[EMAIL PROTECTED] Sent: Sunday, April 17, 2005 1:27 AM To: rietveld_l@ill.fr Bob, A "nice" math. description amenable to RR exists, take a look at JAC(2002) 35, 338-346. "Nice" because the size profile is described by a pV (at "regular" lognormal dispersions) or by a sum of maximum three Lorentzians (at large lognormal dispersions - those 3% that Alan spiked about). The breadths and mixing parameters of pV or of the sum of Lorenzians are calculated analytically from the two parameters of the lognormal distribution, <R> and c. You realize that if approximate the instrumental and the strain profiles by Voigts, it results a sum of three Voigts for the whole profile and for a fast computation, every Voigt can be replaced by our loved TCH pV. Best wishes, Nic > Nic, > Well, I have been tempted from time to time to implement a "log > normal" type distribution in on eof the profile functions. A "nice" math description ameanable to RR would help. > Bob >
