From help-octave-request at bevo dot che dot wisc dot edu  Sat Dec  4 22:27:53 1999
Subject: RE: Dot product (nx1).*(nxm)
From: Mike Miller <mbmiller at taxa dot psyc dot missouri dot edu>
To: Heber Farnsworth <FARNSWORTH at olin dot wustl dot edu>
cc: "'Andre Bonfrer'" <a dot bonfrer at mbs dot unimelb dot edu dot au>,         "'help-octave@bevo.che.wisc.edu'" <help-octave@bevo.che.wisc.edu>
Date: Sat, 4 Dec 1999 22:27:45 -0600 (CST)

On Sat, 4 Dec 1999, Heber Farnsworth wrote:

> p(:,ones(1,m)).*v
> 
> where p is nx1 and v is nxm.  What this does is to multiply v by a nxm
> natrix which has p as every column.


Apparently, Heber's method is faster in this example than the one I
suggested:

octave:1> p=rand(100,1);
octave:2> q=ones(1,50);
octave:3> p2=p*q;
octave:4> t0=cputime; for i=1:1000, p2=p*q; end , cputime-t0
ans = 2.4600
octave:5> t0=cputime; for i=1:1000, p2=p(:,q); end , cputime-t0
ans = 2.0100


Regards,

Mike

-- 
Michael B. Miller
University of Missouri--Columbia
http://taxa.psyc.missouri.edu/~mbmiller/



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