Hi Chris & Brennan, On 15 August 2011 00:59, Brennan Williams wrote: > You can use scipy.stats.truncnorm, can't you? Unless I misread, you want to > sample a normal distribution but with generated values only being within a > specified range? However you also say you want to do this with triangular > and log normal and for these I presume the easiest way is to sample and then > accept/reject. > > Brennan > > On 13/08/2011 2:53 a.m., Christopher Jordan-Squire wrote: > > Hi Andrea--An easy way to get something like this would be > > import numpy as np > import scipy.stats as stats > > sigma = #some reasonable standard deviation for your application > x = stats.norm.rvs(size=1000, loc=125, scale=sigma) > x = x[x>50] > x = x[x<200] > > That will give a roughly normal distribution to your velocities, as long as, > say, sigma<25. (I'm using the rule of thumb for the normal distribution that > normal random samples lie 3 standard deviations away from the mean about 1 > out of 350 times.) Though you won't be able to get exactly normal errors > about your mean since normal random samples can theoretically be of any > size. > > You can use this same process for any other distribution, as long as you've > chosen a scale variable so that the probability of samples being outside > your desired interval is really small. Of course, once again your random > errors won't be exactly from the distribution you get your original samples > from.
Thank you for your answer. Indeed, it appears that a truncated distribution implementation exists only for the normal distribution (in the subset of distributions I need to use). I haven't checked yet what the code for truncnorm does but maybe it might be possible to apply the same approach for other distributions. In any case the sampling/reject/accept approach is the best approach for me, due to my ignorance about statistical things :-) Thank you again. Andrea. "Imagination Is The Only Weapon In The War Against Reality." http://xoomer.alice.it/infinity77/ >>> import PyQt4.QtGui Traceback (most recent call last): File "<interactive input>", line 1, in <module> ImportError: No module named PyQt4.QtGui >>> >>> import pygtk Traceback (most recent call last): File "<interactive input>", line 1, in <module> ImportError: No module named pygtk >>> >>> import wx >>> >>> _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
