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## Re: large sparse matrix

 From: David Bateman Subject: Re: large sparse matrix Date: Tue, 01 Sep 2009 08:07:58 +0200 User-agent: Mozilla-Thunderbird 2.0.0.19 (X11/20090103)

```Carlo de Falco wrote:
```
```
On 31 Aug 2009, at 21:53, David Bateman wrote:
```
```
```
Yes, but the configuration of SuiteSparse in terms of the pivot threshold is the default that TIm Davis sets for Octave and whatever mathworks chose to use for matlab. So don't expect exactly the behavior.
```I see...

```
```In Octave what does

matrix_type(A)
give?
```
```

>> matrix_type (A)
ans = Positive Definite
>>

```
If it doesn't flag your matrix as PD then there might be an issue with the detection of the matrix and PD and the solver used in Octave will be LU.
```
on the other hand what surprises me is that:

>> issparse (B)
ans =  1
>> matrix_type (B)
ans = Rectangular
>> issparse (A)
ans =  1
```
>> mat = [A B' spalloc(rows(A),1,0); B spalloc(rows(B),columns(A),1) E'; spalloc(columns(A),1,1) E 0];
```>> matrix_type (mat)
ans = Full
>> issparse (mat)
ans =  1

why is mat marked as full???

```
```Also, what does the code

[R, p, q] = chol(A);
nnz(R)

```
```
```
```work for Octave and Matlab?
```
```I tried this in Octave, after 30 min it did not finish yet...
I will only be able to try it on Matlab tomorrow.

```
```If so what is the value of NNZ of the factorization in both cases.

Regards
David
```
```

Thanks,
Carlo

```
```What are the sizes of A, B and E?

D.

--
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```

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