Hi, I think we have still included a maximum step size. Which I guess would be used to try and ensure that an integrator does not just completely step over an impulse.
There is nothing to suggest that the tabulation step size is a multiple of the maximum integrator step size, and therefore redundant. Also they will always be misaligned (requiring interpolation) unless the minimum step size is so small that an adaptive scheme never reduces it further. Hopefully your maximum step size and your tabulation step size are much larger than the step size sometimes used by the adaptive integrator. Here forcing results to come back at a fixed spacing forces you not to capture this signal properly in your graphs. This seems really unfortunate, you may have correctly integrated a complicated action potential and then you draw a graph which completely misses it! This seems really bad. Isn't it much better is to concentrate your line segments in your graph in exactly the same places where the adaptive step size system found your solution to be complicated? If an integrator produces "different" results depending on the tabulation step size then it sounds as if it hasn't converged and so the adaptive step size isn't working, maybe your maximum step size needs to be further reduced for the problems you point out about missing the important part? If your tabulation is a multiple of your maximum step size as you suggested then I can't understand how this can happen. (I do realise that there are probably a number of models that are dependent on not being converged.) And if your integration solution is affected by the tabulated result spacing what if you don't want tabulated results? You just want the end integration, then you have to tell your integrator to generate some special tabulation just to get the same final state from your model? After thinking about where the interpolation should be performed, I expect that most integrators will end up interpolating somehow to generate values at the exact grid you specified, I do agree that the integrator may be able to give a far more accurate interpolation, as presumably it has a far finer set of values than the ones returned as results, however requiring a grid, specified in the model metadata, doesn't seem the best way to specify this. I didn't even bring this up yesterday as I was ignored last time I brought it up, but it really seems wrong to me to be forcing your integrator to give results on a grid in every case, and even more concerning to me if as you suggest, the performance of your model is dependent on this grid. However I am not a user or intended user of these ODE integrators. My experience only comes from the ODE integrator that I maintain in CMGUI which is for tracking streamlines and streaklines. So if I am outvoted I'll just take my concerns back into my hole. Shane. _______________________________________________ cellml-discussion mailing list [email protected] http://www.cellml.org/mailman/listinfo/cellml-discussion
