Fast (compiled) routine for element testing and replacement in large matrices?

*To*: mathgroup at smc.vnet.net*Subject*: [mg23929] Fast (compiled) routine for element testing and replacement in large matrices?*From*: "Gareth J. Russell" <russell at cerc.columbia.edu>*Date*: Fri, 16 Jun 2000 00:57:08 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Hello, My first post. I am moving from another software package to Mathematica, and I often work with very large matrices in the context of simulations, so speed is important. Here is a problem for which I would like a serious speed increase. Given a matrix of real numbers, I want to generate a new matrix where values from a certain range are replaced with 1, and the remainder with zero. Matrix size is often on the order of 1000 by 1000 (they are always square). I defined a function that does the comparison using If[], and made it listable: d2wreal[w_,l_,u_] := If[(w>l)&&(D<=u),1,0] SetAttributes[d2wreal,Listable] These are typical times: a = Table[Random[], {i, 1, 100}, {j, 1, 100}]; t = Timing[b = d2wreal[a, 0.2, 0.4]][[1]] 0.46666666666666856 Second a = Table[Random[], {i, 1, 1000}, {j, 1, 1000}]; t = Timing[b = d2wreal[a, 0.2, 0.4]][[1]] 65.55 Second I tried to generate some compiled alternatives myself, but I couldn't find one that was faster. I reckon a 10x speed-up should be possible, possibly more. My other software takes only 0.75 seconds for the 1000 by 1000 matrix function. Can anyone suggest a way to speed this up? Thanks, Gareth ================================================== Dr. Gareth J. Russell NEW ADDRESS and E-MAIL FROM 1ST SEPTEMBER, 1999 Center for Environmental Research and Conservation MC 5556 Columbia University 1200 Amsterdam Avenue New York, NY 10027, U.S.A. Phone: ++1 212 854 5094 Fax: ++1 212 854 8188 E-mail: russell at cerc.columbia.edu WWW: http://web.utk.edu/~grussell (NO CHANGE) OLD ADDRESS (AND STILL MY EMPLOYERS) Department of Ecology and Evolutionary Biology University of Tennessee 569 Dabney Hall Knoxville, TN 37996-1610, USA ==================================================