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Re: About diagonal matrices

From: Daniel J Sebald
Subject: Re: About diagonal matrices
Date: Sun, 01 Mar 2009 13:23:44 -0600
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.3) Gecko/20041020

dbateman wrote:

Well I'm finally somewhere I can write an e-mail from easily, though I
haven't had the time to reread the thread. The issue I considered in the
past like this was operations like "speye(n) .^ 0" or "speye(n) ./ 0" where
the 0.^0 and 0./0 terms of the matrix should create a NaN in the resulting
matrix I hadn't considered the "speye(n) OP NaN" but didn't and don't yet
see why it should be different if the NaN is pre-existing rather than
created by the binary operation, otherwise the NaN values won't propagate
and in fact might very likely disappear. You seem to think, and have
convince John that disappearing NaN's are a good thing so I'll try to reread
the thread and respond again later on.

I think a "default sparse value" solves this, no matter what one thinks the defined 
behavior should be.  Call the indeces assigned the default value the "sparse set".  The 
sparse set could be NaN, while assigned values could also happen to be NaN.

The value of the sparse matrix is when it comes time to use it in operations 
where a full matrix would consume the CPU.  So it does make sense to keep track 
of the sparse set.


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