Hi Spencer, I have copied Woody Setzer. I have no idea whether lsoda can estimate parameters that could take imaginary values. Hank On Jun 11, 2007, at 12:52 PM, Spencer Graves wrote:
> <in line> > > Martin Henry H. Stevens wrote: >> Hi Jeremy, >> First, setting hmax to a small number could prevent a large step, if >> you think that is a problem. Second, however, I don't see how you can >> get a negative population size when using the log trick. > SG: Can lsoda estimate complex or imaginary parameters? Hmm. I have no idea. > >> I would think that that would prevent completely any negative values >> of N (i.e. e^-100000 > 0). Can you explain? or do you want to a void >> that trick? The only other solver I know of is rk4 and it is not >> recommended. >> Hank >> On Jun 11, 2007, at 11:46 AM, Jeremy Goldhaber-Fiebert wrote: >> >>> Hi Spencer, >>> >>> Thank you for your response. I also did not see anything on the >>> lsoda >>> help page which is the reason that I wrote to the list. >>> >>>> From your response, I am not sure if I asked my question clearly. >>> >>> I am modeling a group of people (in a variety of health states) >>> moving through time (and getting infected with an infectious >>> disease). This means that the count of the number of people in each >>> state should be positive at all times. >>> >>> What appears to happen is that lsoda asks for a derivative at a >>> given >>> point in time t and then adjusts the state of the population. >>> However, perhaps due to numerical instability, it occasionally lower >>> the population count below 0 for one of the health states (perhaps >>> because it's step size is too big or something). >>> >>> I have tried both the logarithm trick > <snip> > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting- > guide.html > and provide commented, minimal, self-contained, reproducible code. Dr. Hank Stevens, Assistant Professor 338 Pearson Hall Botany Department Miami University Oxford, OH 45056 Office: (513) 529-4206 Lab: (513) 529-4262 FAX: (513) 529-4243 http://www.cas.muohio.edu/~stevenmh/ http://www.muohio.edu/ecology/ http://www.muohio.edu/botany/ "E Pluribus Unum" ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
