Spencer, Lsoda does not "estimate" any parameters (nlmeODE does parameter estimation). It just computes the solution trajectory, at discrete times, of a dynamical systems (i.e. set of differential equations). It only works with real numbers, as far as I know.
Ravi. ---------------------------------------------------------------------------- ------- Ravi Varadhan, Ph.D. Assistant Professor, The Center on Aging and Health Division of Geriatric Medicine and Gerontology Johns Hopkins University Ph: (410) 502-2619 Fax: (410) 614-9625 Email: [EMAIL PROTECTED] Webpage: http://www.jhsph.edu/agingandhealth/People/Faculty/Varadhan.html ---------------------------------------------------------------------------- -------- -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Spencer Graves Sent: Monday, June 11, 2007 12:53 PM To: Martin Henry H. Stevens Cc: Jeremy Goldhaber-Fiebert; r-help@stat.math.ethz.ch Subject: Re: [R] Fwd: Using odesolve to produce non-negative solutions <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? > 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. ______________________________________________ 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.