Dear all, I noticed two bugs in ode45. I presume that those bugs exist in other ODE solvers as well, such as ode23, ode78, etc. These bugs appear in odepkg 0.6.12.
1. Solving a differential equation with upper interval bound 0 does not work. eg. ode45(@(t,y)y, [-2 0], 2) Fix: The problem is that vdirection is 0, since vdirection is calculated in the following way: 269: vdirection = sign (vtimestop); %# Flag for direction to solve This seems to be a bad idea: One reason is the upper example and if you want to solve a ODE backwards on the interval [2 1], vdirection is positive and thus this ODE won't be solved as well. I'm suggesting to use the following line instead: vdirection = sign(vtimestop - vtimestamp); %# Flag for direction to solve 2. The endpoint of the time slot is not hit exactly if the endpoint is negative. eg f = ode45(@(t,y)y, [0 -1], 1) The endpoint is -1.00019 Fix: Here is a bug in the if-clause that is responsible for hitting the endpoint of the time slot: 316: if ((vtimestamp + vstepsize) > vdirection * vtimestop) In above example you can check that it is doing wrong: vtimestamp = -0.98017 vstepsize = -0.02002 vdirection = -1 vtimestop = -1 Thus -1.00019 > 1 is not true and the vstepsize is not updated such that the endpoint of the time slot is reached. I would suggest to change this line to: if (vdirection * (vtimestamp + vstepsize) > vdirection * vtimestop) All the best, Nils ------------------------------------------------------------------------------ WhatsUp Gold - Download Free Network Management Software The most intuitive, comprehensive, and cost-effective network management toolset available today. Delivers lowest initial acquisition cost and overall TCO of any competing solution. http://p.sf.net/sfu/whatsupgold-sd _______________________________________________ Octave-dev mailing list Octave-dev@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/octave-dev
