On Wednesday, July 10, 2013 4:26:02 PM UTC-4, Flavio Coelho wrote:
>
> Hi,
>
> I am trying to plot the solutions the following system of ODEs
>
> var('t')
> A = function('A',t)
> B = function('B',t)
> de1 = diff(A,t) == -k1*A+k2*B
> de2 = diff(B,t) == k1*A-k2*B
>We're missing some info here. If I make these variables, the commands below don't work at all, so they must be constants of some kind. Can you give values? (Or I can use sol = desolve_system([de1,de2],[A,B],ics=[500,0],ivar=t) as my command.) > sol = desolve_system([de1,de2],[A,B],ics=[500,0]) > show(sol) > solA, solB = sol[0].rhs(), sol[1].rhs() > plot((solA,solB),(t,0,50)) > > however the solution includes A(0) and B(0) as seen below: > > [A(t)=111(6A(0)-5B(0))e(-1120t)+511A(0)+511B(0),B(t)=-111(6A(0)-5B(0))e(- > 1120t)+611A(0)+611B(0)] > How do specify the initial contidions so that my plot command above works? > Now I am getting the following error: > I'd try sol = desolve_system([de1,de2],[A,B],ics=[0,500,0],ivar=t) because t=0 is probably what you implicitly wanted. An initial condition system doesn't necessarily start at t=0, just wherever your information is. > verbose 0 (2424: plot.py, generate_plot_points) WARNING: When plotting, > failed to evaluate function at 200 points. > verbose 0 (2424: plot.py, generate_plot_points) Last error message: > 'unable to simplify to float approximation' > verbose 0 (2424: plot.py, generate_plot_points) WARNING: When plotting, > failed to evaluate function at 200 points. > verbose 0 (2424: plot.py, generate_plot_points) Last error message: > 'unable to simplify to float approximation' > > > -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To post to this group, send email to sage-support@googlegroups.com. Visit this group at http://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/groups/opt_out.
