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Re: About diagonal matrices
From: |
Jaroslav Hajek |
Subject: |
Re: About diagonal matrices |
Date: |
Sun, 22 Feb 2009 10:23:42 +0100 |
On Sat, Feb 21, 2009 at 10:59 PM, Søren Hauberg <address@hidden> wrote:
> lør, 21 02 2009 kl. 16:46 -0500, skrev John W. Eaton:
>> Yes, I understand that it is convenient for many uses for diagonal
>> and sparse matrices to have the properties you want. But I'm also
>> don't like having things like
>>
>> full_matrix == diag_matrix
>>
>> yet
>>
>> diag_matrix * scalar != full_matrix * scalar
>>
>> for some values of scalar.
>
> I don't like this either. But I must say that I really like the reduced
> memory usage that comes with the diagonal matrix type (this has already
> saved me a couple of times). I guess I'm missing the obvious here, but
> couldn't the diagonal matrix class be extended to have a variable that
> holds the value of the non-diagonal elements of the matrix? Usually this
> would be zero, but when the matrix is multiplied with NaN or divided
> with zero, this value would change.
>
> Søren
>
>
Not really. You underestimate the complexity that these demands bring.
Try this in development version:
x = diag ([NaN, 3, 4]); y = diag ([1, 2, 3]);
Now, watch this:
x*y
ans =
NaN 0 0
0 6 0
0 0 12
full (x) * full (y)
ans =
NaN NaN NaN
0 6 0
0 0 12
See? Basically, any combination of rows (or columns) can end as NaN.
But it gets worse:
x = diag ([NaN, 3, Inf]); y = diag ([1, 2, 3]);
full (x) * full (y)
ans =
NaN NaN NaN
0 6 0
NaN NaN Inf
Now imagine the added complexity for the diagonal operations.
One option is to not create a diagonal matrix object at all when NaN
is present. This solves *some* of the issues,
but adds another level of inconsistencies.
--
RNDr. Jaroslav Hajek
computing expert
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz
- Re: About diagonal matrices, (continued)
- Re: About diagonal matrices, John W. Eaton, 2009/02/20
- Re: About diagonal matrices, Jaroslav Hajek, 2009/02/20
- Re: About diagonal matrices, Jaroslav Hajek, 2009/02/20
- Re: About diagonal matrices, dbateman, 2009/02/20
- Re: About diagonal matrices, Daniel J Sebald, 2009/02/21
- Re: About diagonal matrices, Jaroslav Hajek, 2009/02/21
- Re: About diagonal matrices, John W. Eaton, 2009/02/21
- Re: About diagonal matrices, Søren Hauberg, 2009/02/21
- Re: About diagonal matrices, Daniel J Sebald, 2009/02/21
- Re: About diagonal matrices, Jaroslav Hajek, 2009/02/22
- Re: About diagonal matrices,
Jaroslav Hajek <=
- Re: About diagonal matrices, Jaroslav Hajek, 2009/02/22
- Re: About diagonal matrices, Søren Hauberg, 2009/02/22
- Re: About diagonal matrices, Jaroslav Hajek, 2009/02/22
- Re: About diagonal matrices, Jaroslav Hajek, 2009/02/22
- Re: About diagonal matrices, John W. Eaton, 2009/02/22
- Re: About diagonal matrices, Jaroslav Hajek, 2009/02/22
- Re: About diagonal matrices, Jaroslav Hajek, 2009/02/22
- Re: About diagonal matrices, John W. Eaton, 2009/02/22
- Re: About diagonal matrices, John W. Eaton, 2009/02/22
- Re: About diagonal matrices, Jaroslav Hajek, 2009/02/22