On Wed, Sep 15, 2010 at 3:47 AM, Håkan Granath <[email protected]> wrote: > On Sep 15, 3:44 am, Robert Bradshaw <[email protected]> > wrote: >> On Tue, Sep 14, 2010 at 10:44 AM, Håkan Granath >> >> <[email protected]> wrote: >> > On Sep 14, 12:16 am, Robert Bradshaw <[email protected]> >> > wrote: >> >> >> Alastair correctly deduced the issue that it can't tell if the number >> >> is less than or greater than 2, what should it do here? >> >> > I do not know what it should do, but what I would have expected >> > in this case is that continued_fraction would first compute the >> > 53 bit approximation of the input, and then return the continued >> > fraction of that approximation. >> >> If this is what you want, the way to get that is to give it something >> that has 53 bits of precision. > > I completely agree :-) In fact, that is what I tried to do but > got unexpected results. Some background information: > > I compute some quantity a, which is a product of the result of > some high precision (say 1000 bits) numerical computation and an > exact algebraic factor. The number a is expected to be rational, > so to identify it I do something like > > b = a.n(1000) > v = continued_fraction(b) > > However this did not always work, because in some cases b was not > a floating point number as expected but a symbolic expression (a > bug in my opinion, see below). This, I found, can make the > continued fraction computation fail in 2 ways: > > 1. Sometimes, since b is symbolic it is computed with the > default 53 bit precision which is inadequate for my purposes. > > 2. Sometimes v would be the empty list. > > Of course I can work around this by doing something like > > b = a.n(1000).n(1000) > > but, although it works for my code, it is somewhat of a > cludge. Hence I reported the two issues: the topic of this thread > and the issue I found with the n() function: > > http://groups.google.com/group/sage-support/browse_thread/thread/b36c90f1490eac19 > > I hope this makes sense.
Yes, that issue with n() is certainly the root of the problem. - Robert -- To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
