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[sagesupport] Re: ode_solver issues Marshall Hampton Sat Nov 28 18:00:52 2009
I think that's probably a bug. As far as I know, the ode_solver code hasn't been used all that much. When I have personally wanted to numerically solve ODEs I have just written my own RungeKutta 4th order solvers in Cython. If no one else chimes in I will file a ticket for that. Marshall Hampton On Nov 28, 2:11 pm, ryan_n <[EMAIL PROTECTED]> wrote: > Hello all, > > I've just started using Sage, and I'm currently trying to use the > ode_solver class to solve some simple differential equations. I was > having some problems setting up my own program based on this class > until I realized that the number of points in the solution does not > match the number of points requested by the t_span variable. For > example, when I run this script: > _________ > #!/usr/bin/env sagepython > from sage.all import ode_solver > > def f(t, y): > return [y[1], y[0]] > T = ode_solver() > T.function=f > T.y_0=[1, 1] > T.ode_solve(t_span=[0, 10], num_points=100) > print len(T.solution) > T.ode_solve(t_span=[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) > print len(T.solution) > _________ > > I get returned values of 101 and 10, where I would expect 100 and 11. > > I don't know about the first case, but for the second case, the > solution for the last value (10) is missing. I was able to circumvent > this problem by appending a dummy variable to the end of t_span, but > I'm wondering if this is the expected behavior. Is there something > about the solution that I'm missing? I am currently using Sage 4.2.1 > that I built from source in a Gentoo Linux distro. > > In a slightly related aside, I know that y_0 are the initial > conditions, but what if you know the conditions somewhere in the > middle or outside your range of interest (t_span)? Would it be > possible to input known y values as (y,t) tuples that are not > necessarily the first values (and possibly may not get returned in the > solution)? I've tried running the above script and getting the > solution for a particular t value (say t=2), changing y_0 to the > values I got for t=2, and rearrange the t_span list with 2 as the > first value, and the results I get are not what I would expect... Is > there something about solving these types of systems that does not > permit using arbitrary set conditions? (I apologize if this is a > really dumb question. I know very little about ode solving > algorithms.) > > Thanks > > Ryan > > P.S. As this is my first post, I want to thank all of you who started/ > maintain/develop Sage. I've only been using it for a short time, but > I'm extremely happy with what I've seen so far. I look forward to > finding other ways to apply this tool to as many problems as possible.  To post to this group, send email to [EMAIL PROTECTED] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sagesupport URL: http://www.sagemath.org
 [sagesupport] ode_solver issues ryan_n 2009/11/28
 [sagesupport] Re: ode_solver issues Marshall Hampton 2009/11/28 <=
 [sagesupport] Re: ode_solver issues [EMAIL PROTECTED] 2009/11/29
 Re: [sagesupport] ode_solver issues Anthony David 2009/11/29
 [sagesupport] Thanks!!  Re: ode_solver issues ryan_n 2009/11/30
 [sagesupport] Re: Thanks!!  Re: ode_solver issues Jason Grout 2009/11/30