1. the concept that Maxima fails to "preserve precision" that seems to be bandied about here doesn't seem to me to make much sense. You have 2 numbers of different precisions and you operate on them. What is supposed to be preserved?
2. If the MPFR fraction has N bits, then ?fpprec:N will be a Maxima bigfloat with N bits in the fraction (part of a float). 3. In my view the tool that Maxima provides should be doing accurate arithmetic on rational numbers that happen to have powers-of-2 denominators or multipliers such that the result of the arithmetic is the rational number that is closest to the mathematical answer, with the specified number of bits in the fraction. Any notion that a bigfloat represents some kind of epsilon + or - is BAD. If you want to carry around another number that makes the exact bigfloat into an interval, then you should feel free to do so. Don't expect the bigfloat to do it for you magically. Mathematica tries that, and it leads to terrible mistakes. No one else does significance arithmetic, and I strongly suggest Sage not do it. On Thursday, June 14, 2012 9:14:50 PM UTC-7, Nils Bruin wrote: > > On Jun 13, 7:32 pm, rjf <fate...@gmail.com> wrote: > > If you want a Sage number X of n (binary) bits precision to be converted > to > > a Maxima bigfloat of n bits, > > then you can do this. > > First in Sage compute Xrat which is an exact rational that is equal to > X. > > It could be computed > > by something like (some integer) times 2^(some power): > > > > then in maxima, you utter the program fragment: > > > > block([?fpprec:n], bfloat(Xrat)) > > > > note ?fpprec is the BINARY version of fpprec. > > For the benefit of people who want to work on this: > > There is code on > > http://trac.sagemath.org/sage_trac/ticket/11643 > > for converting between MPFR and maxima BFLOAT. The problem that needs > to be figured out is how to set fpprec to a reasonable value. set ?fpprec. You can extract the precision of a bigfloat in Maxima.. ?caddar(1.0b0) for example. or if you hate that c..d...r business , do ?third(?first(1.0b0)). the precision is in the 3rd spot of the header. -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
