From: <Setzer.Woodrow_at_epamail.epa.gov>

Date: Mon, 11 Jun 2007 14:30:55 -0400

R-help_at_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. Received on Mon 11 Jun 2007 - 18:38:40 GMT

Date: Mon, 11 Jun 2007 14:30:55 -0400

By the way, if someone could forward the original question to me (I'm
subscribed to but not currently receiving R-help, as I found I was
spending too much time reading it!) I might think of something more
useful. (alternatively, when was it posted; I can find it on gmane,
too).

Woody

R. Woodrow Setzer, Ph. D.

National Center for Computational Toxicology
US Environmental Protection Agency

Mail Drop B205-01/US EPA/RTP, NC 27711

Ph: (919) 541-0128 Fax: (919) 541-1194

"Martin Henry H. Stevens" <HStevens_at_muohio To .edu> Spencer Graves <spencer.graves_at_pdf.com> 06/11/2007 01:02 cc PM Jeremy Goldhaber-Fiebert <JGOLDHAB_at_hsph.harvard.edu>, R-Help <r-help_at_stat.math.ethz.ch>, Woodrow Setzer/RTP/USEPA/US_at_EPA Subject Re: [R] Fwd: Using odesolve to produce non-negative solutions

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_at_stat.math.ethz.ch mailing list
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**> 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"

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