Denis Nikiforov schrieb: > I need to plot several trajectories of a solutions of ODE like here: > http://www.wam.umd.edu/~petersd/246/matlabauton.html > > hold on > for a1=-7:2:5 > for a2=-7:2:1 > [ts,ys] = ode45(g,[0,4],[a1;a2]); > plot(ys(:,1),ys(:,2)) > [ts,ys] = ode45(g,[0,-4],[a1;a2]); % Doesn't work in octave > plot(ys(:,1),ys(:,2)) > end > end > hold off > > But ode45 doesn't work for decreasing time > [ts,ys] = ode45(g,[0,4],[a1;a2]); - works fine > [ts,ys] = ode45(g,[-4,0],[a1;a2]); - gives the same result as above > [ts,ys] = ode45(g,[0,-4],[a1;a2]); - doesn't work as it works in matlab > > So I can plot only half of solution and trajectory is incomplete. > Also if a result grows too fast I couldn't plot the trajectory for specific > initial conditioins at all, because of error: > > Solving has not been successful. The iterative integration loop exited at > time > t = 1.523467 before endpoint at tend = 4.000000 was reached. This may happen > if the stepsize grows smaller than defined in vminstepsize. Try to reduce the > value of "InitialStep" and/or "MaxStep" with the command "odeset". > > Could you fix solvers to make their behaviour more close to matlab one? > Matlab > 1) solves ODE for decreasing time and 2) shows only warning if a solution > becomes too big. > > Thanks )
Hi Denis, 1) In general yes, but right now I'm very sorry that (at least) I don't have the time to do it. But, can you provide a small example for a function 'g' with a reference solution at t=-4 and the initial values needed? 2) What exactly do you mean here? If you are talkin' about the error that you've posted then I would suggest to reduce "InitialStep" and/or "MaxStep"?! Thomas ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ Octave-dev mailing list Octave-dev@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/octave-dev
