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> the output of ode45 into the spline command with the third input set to t. > suggest you run ode45 with for the time slot, and then put > If you want to get octave ode45 to do the same as matlab ode45, I > spline to figure out the value of the function at all the time slots. > the ODE the same way irrespective of the length of t, and then uses a > I am told that Matlab ode45 works differently. > determine the time intervals used by the time solver. > If t contains more than two elements, then it uses those elements to Then it solves the ODE from time t(1) to t(2). > intervals set so that it can be sure that RelTol and AbsTol are > If t contains only two elements, then ode45 solves the ode at time > ode45.m shows that you get the above warning messages if the input t I think the documentation provided by "help > latter case, ode45 can chose the grid points in order to match the > time parameter t instead of an interval (). > I guess "time stamps" means that you have a vector of time instances as > documentation I can find indicates that 'time stamps' have to do with > What do these messages mean? How do I properly set the tolerance? The > warning: Option "AbsTol" will be ignored if fixed time stamps are given > warning: Option "RelTol" will be ignored if fixed time stamps are given > also need to vary ode45's tolerance level, but I'm getting the
> I'm getting different results from Octave's ode45 than from Matlab's. On Fri, at 9:59 PM, Stephen Montgomery-Smith wrote:
#Ode45 matlab code#
MCE 372 Engineering Analysis Example Code The solutions from either code are identical and the plot is shown below First Order ODE Solution Using ode45 with User Function Method Example From Gilat 4th Ed. Repeated calls may create even more inefficiencies. Two example MATLAB codes using the ode45 solver are shown below. In that way, you can still set the tolerance level. Note that Octave's ode45 is saving so many time steps that *it runsĬonsiderably slower* on a much more powerful machine than Matlab doesĪnother possible workaround (for anyone who finds this thread) might be toĬall Octave's ode45 repeatedly with incremental time spans, using the finalĬonditions of the each call as the initial conditions of the followingĬall. Have the ability to solve like Matlab's does? Is it not possible to set the Interpolation, but it does interpolate to find the value at the time slots).ĭo I understand your last paragraph to imply that Octave's ode45 does not Your understanding of Matlab is correct (well, I don't know how it does the That is how I understand Octave's ode45 help (now). You might look at the discussion near the beginning of Section 7 of this paper, and the references given there. (2) Wrote the state space correctly.Thanks, Stephen. \begingroup I don't know if ODE45 is intended to work for problems with singularities. I'm not used to using ode45 for differential equations, but I just want to know if I
I'm currently trying to figure out if the part that is separated from the other part of the code is written in the correct state space form. We are inputting, the mass of the collar sliding along a friction-less rod, the mass of the partical hanging from the pendulum, spring constant, some initial length of the pendulum, how much time we want, an interval of time, and (not really sure what frames per second to put really). So I am tasked to use ode45 to solve 3 equations of motions and then create an animation of the differential equation, which is a pendulum fixed to a moving collar moving horizontally, with a mass attached to the end.