On Thu, Dec 31, 2009 at 9:13 PM, Tim Daly <d...@axiom-developer.org> wrote: > Dr. David Kirkby wrote: >> rjf wrote: >> >>> On Dec 31, 11:15 am, "Dr. David Kirkby" <david.kir...@onetel.net> >>> wrote: >>> >>> >>>>> RJF >>>>> >>>> The point you are missing is that we want to compare the output what Sage >>>> prints >>>> to a human. >>>> >>>> >>> The point you are missing is that the following item, which presumably >>> could be printed by Sage, >>> is perfectly readable to a human: >>> >>> 6121026514868073 * 2^(-51). >>> >>> It exactly dictates the bits in an IEEE double-float, and does not >>> require any conversion from binary >>> to decimal. It does not need rounding. This kind of representation >>> does not have any hidden unprinted digits. It does not ever need to >>> be longer because of delicate edge conditions of certain numbers. >>> >>> It happens to evaluate to >>> APPROXIMATELY 2.718281828459045 >>> >> >> Sure, Sage could print that. It would also be worth printing the sign bit, >> so we >> could verify the values of >> >> 1) Sign bit >> 2) Significand >> 3) Exponent. >> >> All of those could be correct. But there is still the software which does the >> non-trivial task of converting that into the base 10 representation used by >> humans. Then in additon to that, there is the software which takes a base 10 >> number, shows it with the Sage prompt, adding carriage returns etc where >> necessary. All of these can go wrong. >> >> I would think in an almost ideal world, the test would be done at a higher >> level, using hardware/software which checked what the monitor actually >> displayed. That's not quite as easy to do though. >> >> Even better would be some way to scan the brain of the user to see what >> he/she >> believes Sage is showing. Perhaps we use a font that is not very good, so >> despite being displayed properly, it misunderstood. >> >> Given most of time people want to see a base 10 representation of a number, >> and >> not a base 2, base 16 or IEE 754 representation, I believe most testing >> should >> be done at the base 10 level. >> >> If there is a reason for testing the IEEE 754 representation as first choice, >> then you have yet to convince me of it. >> >> >> Dave >> >> >> > Dave, > > Axiom has the same issues. > > My take on this is that what you check depends on the reason you are > checking. > If you are generating the output for human use (e.g. a table) then you > want decimal. > If you are generating the output for regression testing (e.g. checking > the answers on > multiple hardware) then you probably want Fateman's solution. > > Tim
The output is used both for human use and for regression testing. Its primary use is human -- it's an example in the Sage reference manual: sage: float(e) 2.7182818284590451 This is something a user will look at when reading the documentation for some function. It illustrates what happens when they convert the symbolic constant e to float. William -- 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
