On Tue, Dec 9, 2008 at 4:48 PM, Tim Lahey <[EMAIL PROTECTED]> wrote: > > > On Dec 9, 2008, at 7:38 PM, William Stein wrote: > >> >> This is not the answer. Look at this example: >> >> sage: srange(0,1.1,0.1,include_endpoint=True) >> [0.000000000000000, >> 0.100000000000000, >> 0.200000000000000, >> 0.300000000000000, >> 0.400000000000000, >> 0.500000000000000, >> 0.600000000000000, >> 0.700000000000000, >> 0.800000000000000, >> 0.900000000000000, >> 1.00000000000000, >> 1.10000000000000, >> 1.20000000000000] >> >> That's not right no matter what. The documentation says: >> " Return list of numbers a, a+step, ..., a+k*step, >> where a+k*step < b and a+(k+1)*step > b." >> where a,b are the first two inputs. >> >> Thus the implementation of srange is simply buggy because the person >> (me!) who implemented didn't take proper care of how floating point >> numbers behave. >> > > I ran across this in some timestepping code I wrote for a ODE solver > for systems of second order ODEs. The general trick I used is to set > the first n-1 terms based upon the formula and set the final one to > the endpoint. It means that the final one may be shorter, but that way > it always ends at the set endpoint.
Any chance you could dive in and fixe srange? It's a pure Python function in sage/misc/misc.py William --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
