[R-sig-dyn-mod] Vectorizing

[E Michael Foster]

This is all very helpful--thanks to both you and Thomas 

Believe me, I'm not going to try ABM with R--that seems way above my pay grade--I'll be happy if I can do some basic simulations of populations with R.  (I leave my ABM work to AnyLogic and commercial packages)

Thanks again --

E. Michael Foster
Professor, Department of Health Care Organization and Policy 
School of Public Health 
The University of Alabama at Birmingham 


-----Original Message-----
From: r-sig-dynamic-models-bounces at r-project.org [mailto:r-sig-dynamic-models-bounces at r-project.org] On Behalf Of Stephen Ellner
Sent: Monday, November 07, 2011 9:39 AM
To: r-sig-dynamic-models at r-project.org
Subject: [R-sig-dyn-mod] Vectorizing

Unfortunately, the only method I know for mastering vectorizing is practice, practice, practice, after looking at the pointers that Thomas suggested. The PDE application that I described worked in R because it was possible to compute once-and-for-all matrices such that all the calculations needed to compute approximate spatial derivatives were done with two matrix-vector multiplications (one each for first and second derivatives). I have very little experience with ABMs, so I don't know how frequently there are tricks like that which make loops go away. Maybe others on this list can provide some examples? 

Steve Ellner

>Date: Sun, 6 Nov 2011 07:34:24 -0600
>From: E Michael Foster <emfoster at uab.edu>
>To: Special Interest Group for Dynamic Simulation Models in R
>        <r-sig-dynamic-models at r-project.org>
>
>Thanks so much for taking the time to respond.  
>
>This is kind of what I feared and I know about the benefits of vectorizing calculations.  
>My difficulty is that the idea of loops is so drilled into my brain
>
>Know of a good resource for mastering vectorizing calculations?  
>Googling, I certainly can see plenty of instances where folks are 
>asking for help on technical problems--
>
>E. Michael Foster
>Professor, Department of Health Care Organization and Policy School of 
>Public Health The University of Alabama at Birmingham

Stephen P. Ellner (spe2 at cornell.edu)
Department of Ecology and Evolutionary Biology Corson Hall, Cornell University, Ithaca NY 14853-2701
Phone (607) 254-4221    FAX (607) 255-8088
* This is my work email. I try not to read it at other times *

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