On Nov 20, 2007 12:28 PM, Ted Kosan <[EMAIL PROTECTED]> wrote:
> Does anyone have any thoughts on why the solve() function this program
> returns an empty list?:
>
> sage: var('t')
> sage: a = .004*(8*e^(-(300*t)) - 8*e^(-(1200*t)))*(720000*e^(-(300*t))
> - 11520000*e^(-(1200*t))) +.004*(9600*e^(-(1200*t)) -
> 2400*e^(-(300*t)))^2
> sage: print a(t=.000411)
> sage: show(plot(a,0,.002),xmin=0, xmax=.002)
> sage: solve(a==0,t)Maxima stupidly decides there is no solution. This is clearly a bug. This is the sort of bug in Sage that is very difficult for us to fix since it's really a bug in Maxima, and it's entirely possible that maxima developers would not even call it a bug. But clearly it is, since it's a mathematically incorrect result. Alternatively, maybe there is more to using solve than I understand, and a maxima expert could explain how to use the maxima solve function in a more robust manner ?! Here's what happens when you try this in Maxima directly: sage: !maxima Maxima 5.13.0 http://maxima.sourceforge.net Using Lisp CLISP 2.41 (2006-10-13) Distributed under the GNU Public License. See the file COPYING. Dedicated to the memory of William Schelter. This is a development version of Maxima. The function bug_report() provides bug reporting information. (%i1) solve(0.004*(8*%e^-(300*t)-8*%e^-(1200*t))*(720000*%e^-(300*t)-11520000*%e^-(1200*t))+0.004*(9600*%e^-(1200*t)-2400*%e^-(300*t))^2=0, t) ; `rat' replaced 0.004 by 1/250 = 0.004 `rat' replaced 0.004 by 1/250 = 0.004 (%o1) [] I strongly encourage you to report this to the maxima list, if you agree that it is a bug in Maxima. I think in the long-run Sage will have to completely implement its own solve function, which is better than Maxima's. Thoughts from Ondrej-sympy would be appreciated here. > And why the solve() function in this program hangs?: > > sage: var('t') > sage: v = 0.004*(9600*e^(-(1200*t)) - 2400*e^(-(300*t))) > sage: show(plot(v,0,.002),xmin=0,xmax = .002) > sage: solve(v == 0,t) Here maxima also gives the wrong answer: sage: maxima(v == 0) 0.004*(9600*%e^-(1200*t)-2400*%e^-(300*t))=0 sage: maxima(v == 0).solve(t) [] Just to emphasize that in my opinion this is *definitely* a bug, I've entered this into the tracker: http://trac.sagemath.org/sage_trac/ticket/1235 But this might be pretty hard to fix soon. Making sure we are well aware of it, though, is critically important if we are to push Sage to be truly professional level in non-algebraic areas... -- William --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-support@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-support URLs: http://sage.math.washington.edu/sage/ and http://sage.scipy.org/sage/ -~----------~----~----~----~------~----~------~--~---
