I jumped over from the sage-support group, where I had posted a question about graphing x^(1/3). Alex Ghitza's response to me made more sense when I read the background discussion here.
I am experiencing the same inconsistency revealed in the latter part of this discussion. I am also running Sage locally on a MacOS X PPC G4 machine, and it graphs plot(x^(1/2)) just as I expected. I was stumped when I uploaded my worksheet to sagenb.org, and got the same error message for the square root function, which I thought was restricted in some way to cube roots. (I'm a novice.) Ditto on the inconsistency of plotting log(x) and math.sqrt(float(-1)) -- which produces nan on my machine, and an error message on sagenb.org. I thoroughly agree with kcrisman's reasoning that a implied real range is a feature, not a bug, for plotting. Andy On Feb 21, 7:03 am, kcrisman <[EMAIL PROTECTED]> wrote: > Sorry I never attached the graphic - it's on my desktop, but the > Google Groups help leads me to believe someone has turned off file > posting on this group (on sage-support it seems to still be available, > though, given recent posts). > > > > > OK, now I'm curious. I still get errors (with 2.10.1 and with > > 2.10.2.alpha0), as do a couple of people I asked to test this on IRC. > > > What OS/architecture are you using? > > Mac OSX.4, PowerPC G4 > > > Do you get different results than this: > > sage: import math > > sage: math.sqrt(float(-1)) > > --------------------------------------------------------------------------- > > <type 'exceptions.ValueError'> Traceback (most recent call > > last) > > > /home/cwitty/sage/<ipython console> in <module>() > > > <type 'exceptions.ValueError'>: math domain error > > Yes, I do! > > sage: import math > sage: math.sqrt(float(-1)) > nan > > My computer's native Python installation also provides: > > Python 2.3.5 (#1, Mar 20 2005, 20:38:20) > [GCC 3.3 20030304 (Apple Computer, Inc. build 1809)] on darwin > Type "help", "copyright", "credits" or "license" for more information.>>> > import math > >>> math.sqrt(float(-1)) > > nan > > So presumably plot is somehow using this. Personally, I think this is > a feature, not a bug - if one specifies an implied real range for a > function, non-real outputs should just be ignored, which should avoid > the messing up of internal calculations that having a "real" method or > something would imply. For instance, on the same computer, the > following plots something nice and without complex branches or > something weird like that: > > sage: show(plot(log(x),-5,5)) > > While looking into this I discovered: > > sage: log(0) > --------------------------------------------------------------------------- > <type 'exceptions.TypeError'> > [lots of stuff] > <type 'exceptions.TypeError'>: error evaluating "log(0)": > Error executing code in Maxima > CODE: > log(0); > Maxima ERROR: > log(0) has been generated. > > Presumably log(0) should provide a more helpful (and much shorter) > error message. And what does this phrase, "log(0) has been > generated," mean? > > - kcrisman --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
