Re: large sparse matrix

[Carlo de Falco]

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