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Re: strange problem
From: |
Tomer Altman |
Subject: |
Re: strange problem |
Date: |
Fri, 28 Nov 2003 01:11:14 -0800 (PST) |
Laurent, thanks for reminding me of a question I wanted to ask:
If Octave uses LU-decomposition for matrix multiplication, does it
also "cache/memoize" the resulting decomposition, so that further
multiplications are only O(n^2), and not O(n^3) if done from scratch?
Also, are interpreted results "cached/memoized" in general? This could
save time in referentially-transparent which are relatively expensive
to call.
Just curious,
~Tomer
On Nov 28, 2003 at 10:01am, Laurent Jacques wrote:
ljacqu >Date: Fri, 28 Nov 2003 10:01:28 +0100
ljacqu >From: Laurent Jacques <address@hidden>
ljacqu >To: address@hidden
ljacqu >Subject: Re: strange problem
ljacqu >Resent-Date: Fri, 28 Nov 2003 03:01:31 -0600
ljacqu >Resent-From: address@hidden
ljacqu >
ljacqu >On Friday 28 November 2003 00:03, Geraint Paul Bevan wrote:
ljacqu >| The number -2.0817e-17 is -0.000000000000000020817, which is very,
very
ljacqu >| close to zero. The error is due to the way that numbers are
represented
ljacqu >| in computers.
ljacqu >
ljacqu >Of course but I think that the question was:
ljacqu >
ljacqu >Why the top-left entry of
ljacqu > [1,100;0,1]*[1,0;(-1/100),1]
ljacqu >is
ljacqu > -2.0817e-17
ljacqu >while octave returns the true 0 if you enter
ljacqu > 1 + (100*-1/100)
ljacqu >
ljacqu >Does Octave perform some LU decomposing of matrix to realize matrix
ljacqu >multiplication ?
ljacqu >This could explain the difference between the two results.
ljacqu >
ljacqu >Laurent.
ljacqu >
ljacqu >
ljacqu >
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ljacqu >Octave is freely available under the terms of the GNU GPL.
ljacqu >
ljacqu >Octave's home on the web: http://www.octave.org
ljacqu >How to fund new projects: http://www.octave.org/funding.html
ljacqu >Subscription information: http://www.octave.org/archive.html
ljacqu >-------------------------------------------------------------
ljacqu >
ljacqu >
-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.
Octave's home on the web: http://www.octave.org
How to fund new projects: http://www.octave.org/funding.html
Subscription information: http://www.octave.org/archive.html
-------------------------------------------------------------
Message not available
strange problem, John W. Eaton, 2003/11/28