comp.lang.idl-pvwave archive - RDF feed
type: channel
description: Messages from Usenet group comp.lang.idl-pvwave, compiled by Paulo Penteado
items: Re: Matrix expansion performance

Re: Matrix expansion performance
type: item
description: In article <d28tre$j32$1@pegasus.fccn.pt>, "Ricardo Bugalho" <rbugalho@ibili.uc.pt> wrote: > Hi, > I have a matrix A (m,n) is and I want to create a matrix B(m,n,p) such > that each B(*,*,i) slice equals A. p is very large and n is usually > smaller than m so I have: > B=bytArr(m,n,p) > C=byteArr(p) + 1 > FOR i = 0, n-1 DO B[*,i,*] = REFORM(A[*,i]) # p Quite fast, but not > enough for my needs. Any one has better sugestions? Still stuck in IDL > 5.4, by the way. > Thanks, > Ricardo > Assuming your code was wrong, and that #p should be #C. A bit of reform magic will do what you want. http://www.dfanning.com/tips/rebin_magic.html e.g. b=rebin(reform(a, [m, n,1]), [m,n,p]) Chris.
creator: Chris Lee
date: 2005-03-28T13:43:39-00:00

Re: Matrix expansion performance
type: item
description: In article <d28tre$j32$1@pegasus.fccn.pt>, "Ricardo Bugalho" <rbugalho@ibili.uc.pt> wrote: > Hi, > I have a matrix A (m,n) is and I want to create a matrix B(m,n,p) such that > each B(*,*,i) slice equals A. p is very large and n is usually smaller than > m so I have: > > B=bytArr(m,n,p) > C=byteArr(p) + 1 > FOR i = 0, n-1 DO B[*,i,*] = REFORM(A[*,i]) # p This should be quite fast, if I understand your problem correctly: B = BYTARR(m,n,p) FOR k = 0, p-1 DO B[0,0,k] = A This will avoid subscript arrays and should access memory efficiently on most machines. Ken Bowman
creator: Kenneth P. Bowman
date: 2005-03-28T13:50:00-00:00

Re: Matrix expansion performance
type: item
description: "Kenneth P. Bowman" <kpb@null.com> wrote in message news:kpb-E62DD6.07500028032005@news.tamu.edu... > In article <d28tre$j32$1@pegasus.fccn.pt>, > "Ricardo Bugalho" <rbugalho@ibili.uc.pt> wrote: > >> I have a matrix A (m,n) is and I want to create a matrix B(m,n,p) such >> that >> each B(*,*,i) slice equals A. p is very large and n is usually smaller >> than >> m so I have: > > This should be quite fast, if I understand your problem correctly: I think I didn't make clear the ranges of m,n and p. In the problem I have at hand, m is always 8, n is usually 5 (min 1, max 16) and p is in the range of 10,000 to 100,000. Looping over p is a BadThing(tm) due to IDL's high interpretation overhead. > > B = BYTARR(m,n,p) > FOR k = 0, p-1 DO B[0,0,k] = A > > This will avoid subscript arrays and should access memory efficiently on > most machines.
creator: Ricardo Bugalho
date: 2005-03-29T09:55:29-00:00

Re: Matrix expansion performance
type: item
description: On 29.03.05 at 10:55 +0100, Ricardo Bugalho wrote: > I think I didn't make clear the ranges of m,n and p. > In the problem I have at hand, m is always 8, n is usually 5 (min 1, max 16) > and p is in the range of 10,000 to 100,000. > Looping over p is a BadThing(tm) due to IDL's high interpretation overhead. The method that Chris Lee suggested does not use loops. But I think there is no need for any call to REFORM. And the dimension arguments to REBIN must be scalars in IDL 5.4. A simple b = rebin(a, m, n, p, /sample) should therefore work (and, hopefully, be fast enough for your purposes). Timm -- Timm Weitkamp <http://people.web.psi.ch/weitkamp>
creator: Timm Weitkamp
date: 2005-03-30T08:22:46-00:00

Re: Matrix expansion performance
type: item
description: I used Chris' method. However, I've been having some problems posting and my thanks to him got lost. "Timm Weitkamp" <dont.try@this.address> wrote in message news:Pine.LNX.4.44.0503301010060.7505-100000@localhost.local domain... > > The method that Chris Lee suggested does not use loops. But I think there > is no need for any call to REFORM. And the dimension arguments to REBIN > must be scalars in IDL 5.4. A simple
creator: Ricardo Bugalho
date: 2005-03-30T12:18:32-00:00

Re: Matrix expansion performance
type: item
description: In article <Pine.LNX.4.44.0503301010060.7505-100000@localhost.localdomain>, "Timm Weitkamp" <dont.try@this.address> wrote: > On 29.03.05 at 10:55 +0100, Ricardo Bugalho wrote: >> I think I didn't make clear the ranges of m,n and p. In the problem I >> have at hand, m is always 8, n is usually 5 (min 1, max 16) and p is in >> the range of 10,000 to 100,000. Looping over p is a BadThing(tm) due to >> IDL's high interpretation overhead. > The method that Chris Lee suggested does not use loops. But I think > there is no need for any call to REFORM. And the dimension arguments to > REBIN must be scalars in IDL 5.4. A simple > > b = rebin(a, m, n, p, /sample) > should therefore work (and, hopefully, be fast enough for your > purposes). Timm > My first reaction was "when did that happen?", I tried it without the reform, and it works...except IDL> help, rebin(fltarr(4,5),[7,4,5,6]) % REBIN: Result dimensions must be integer factor of original dimensions doesn't work (6.1.1 Linux), but the reform version does IDL> help, rebin(reform(fltarr(4,5),[1,4,5,1]),[7,4,5,6]) <Expression> FLOAT = Array[7, 4, 5, 6] So my world-view isn't completely shattered :) Chris.
creator: Chris Lee
date: 2005-03-30T15:21:02-00:00