Thanks much, that helps and I am pretty sure I understand what is going on!
On Monday, March 24, 2014 10:49:18 AM UTC-4, Peter Bruin wrote: > > Hello, > > > I am working on a Z80 project and I needed 72 bits of precision for 64 > > elements of the form log2(1+2^-i) (so log2(3/2), log2(5/4),...). I > > needed to convert these to hexadecimal, and it worked until I tried > > the following for i=56: > > int(256*log(1+2^-56,2)) > > > > This returns 1, when in fact it should be 0. Actually, instead of > > multiplying by 256, multiplying by 65536, or 600, or many other > > numbers would also return the integer part as 1. > > > > As a note, I used RealField(80) as my precision. > > Typing log(1 + 2^-56, 2) gives the result as a symbolic expression, not > as an element of a real field. Applying int() to this internally uses a > RealIntervalField with 53 bits of precision, which is not enough in this > case. Here is a way to get the desired precision: > > sage: x = RealField(80)(256*log(1+2^-56,2)) > sage: x > 5.1254824061038682620123e-15 > sage: int(x) > 0 > > Peter > > -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To post to this group, send email to sage-support@googlegroups.com. Visit this group at http://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/d/optout.
