There are a whole bunch of issues raised in the context of bool(x>0) and some mention of what Maxima does, in that thread from 4 years ago.
But the description of what Maxima* actually does* was essentially missing from the discussion. As is often the case when several different conflicting opinions emerged in the design community for Macsyma/ Maxima , a flag is available to choose a design Thus is (a>0) returns unknown. prederror:true; is(a>0) produces an error "unable to evaluate predicate a>0" There are probably other options that have to do with domain:real or domain:complex, and assumptions on individual names. It is also possible for the system to return an unevaluated conditional as if (a>=0 then 1 else 2 returns unevaluated. (though is (a>0) returns unknown ) [note difference between is() and if..... ] I suppose (but have not observed this) that the unevaluated 'if' could be simplified. e.g. if (a^2=a) then 1 else 2 might be simplified to if (a=1)or(a=0) then 1 else 2 Now if you wanted to have a program that evaluated a boolean expression where each value was a canonical True or False, and objected somehow otherwise, that might be a different functionality, and certainly WAY simpler than what people seem to expect in a computer algebra system. You could also have a 3 way branching if: yes/no/unknown. if a then be else c otherwise d. Perhaps related, Note also that for IEEE standard floats with NaNs (Not a numbers), of which there are a huge number ..all comparisons return false. That is for N a NaN and X a float, all these are false: N>x N<x N=x even if x is, as a binary string the same NaN, a float comparison returns false This line of reasoning would suggest that all comparisons between numbers and things that are not-a-number, as for example symbols, or formulas, or complex numbers should return false. But that is perhaps pushing the paradigm of floats dominating everything too far. [ the idea would be that everything is a floating-point computation by default, but other stuff, like symbols, can be represented via NaNs. Matlab could have done this, maybe, but instead, last I looked, used what amounted to strings for non-numbers. Maybe that's changed to be object-oriented structure stuff. Maybe they use NaNs for structures?? I doubt it...] RJF On Sunday, February 19, 2017 at 9:07:19 AM UTC-8, Jakob Kroeker wrote: > > In my opinion not this only particular case but the current bool() design > in sage is a tremendous failure. > This was already discussed on sage-devel several times. > > Here is one of that threads: > https://groups.google.com/d/msg/sage-devel/vNxnHSeRBW4/UkaBOPGYT0QJ > > Jakob > > Am Sonntag, 19. Februar 2017 12:56:49 UTC+1 schrieb Daniel Krenn: >> >> Dear all, >> >> I am surprised by >> sage: bool(I < 1) >> True >> >> Best Daniel >> > -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
