Re: About diagonal matrices

[Jaroslav Hajek]

On Sun, Mar 1, 2009 at 8:23 PM, Daniel J Sebald <address@hidden> wrote:
> 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.

No, it doesn't. At least not completely - just the simple cases. See
my previous examples about this. And it would make the sparse
operations more complicated and probably less efficient.
You are, obviously, free to propose a detailed implementation. But
please be more specific.

> 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.
>

Huh? I don't understand.

> Dan
>



-- 
RNDr. Jaroslav Hajek
computing expert
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz