Re: [Help-gsl] Declaring GSL Matrices and Vectors Within a Structure

[Matthew Boulton]

So instead of stamps[i].vectors, I should use say stamps_vectors as a 
GSL matrix (as I have to take into account the stamps elements and the 
vectors elements I'm assuming?). I'm basically re-writing someone else's 
code to use the GSL and it seems to be putting the different elements of 
stamps[i] to use later in the programme. If I ignore the stamps 
structure stuff and just use vectors and area as GSL vectors this may 
cause me problems when each separate value for each stamps[i] element is 
read.

So my first thought was to convert something like stamps[i].area which 
would become just a GSL vector called 'area', to a GSL matrix called 
'stamps_area'. This gives me back my 2d structure. However, I will be 
stuck when I come to something like 'stamps.vectors' as vectors will 
need to be a GSL matrix, so 'stamps_vectors' would need to be some kind 
of 3D matrix, which I'm not sure is even possible!

I'm happy to implement the above strategy for everything else, but 
unless I can find an alternative or a 3D matrix function I will be 
unable to do so for stamps.vectors.

Kind Regards,

Matt


John Gehman wrote:
> Hi Matt,
>
> #Declare with
> gsl_vector *vectors;
> gsl_vector *area;
>
> #Then when you know their size
> vectors = gsl_vector_alloc(size_v);
> area = gsl_vector_alloc(size_a);
>
> gsl_vector element precision is double by default. Some posts lately 
> have addressed the virtues of adapting for float precision when double 
> is unnecessary. Also you may also want to look into analogous 
> gsl_matrix structures. There certainly are cases where you want to 
> have a express a conceptual matrix as a mathematical vector, but if 
> you're doing linear algebra on your *vectors at all, look into the 
> gsl_matrix.
>
> Cheers,
> john
>
> On 25/08/2007, at 9:07 PM, Matthew Boulton wrote:
>
> > Hello. I'm wondering what is the best way to declare a GSL vector or 
> > matrix contained within a structure?
> >
> > For example, at present I have a structure defined as follows:
> >
> > typedef struct
> > {
> >  int       x,y;
> >  DATA_TYPE **vectors;
> >  DATA_TYPE *area;
> >  double    **mat;
> >  double    *scprod;
> >  double    sum;
> >  double    chi2;
> >  double    norm;
> >  double    diff;
> >  char      keep;
> > } stamp_struct;
> >
> > stamp_struct *stamps;
> >
> > where DATA_TYPE defines a double precision variable. Now currently 
> > the code allocates memory using malloc for the vectors and matrices. 
> > For example:
> >
> > for( i = 0 ; i < stamp_number ; i++ )
> > {
> >    for( j = 0 ; j < ncomp_kernel + nbg_vectors ; j++ )
> >    {
> >    stamps[i].vectors = (DATA_TYPE **)malloc( ( ncomp_kernel + 
> > nbg_vectors ) * sizeof(DATA_TYPE *)  );
> >    stamps[i].vectors[j] = (DATA_TYPE *)malloc( stamp_size * 
> > stamp_size * sizeof(DATA_TYPE) );
> >    }
> > }
> >
> >
> > I'm assuming the structure declaration "DATA_TYPE **vectors;" can be 
> > replaced with "gsl_matrix *vectors". However I'm not sure how I can 
> > replace the above code. Usually I would have something like the 
> > following:
> >
> >
> > gsl_matrix *stamps.vectors = gsl_matrix_calloc( ncomp_kernel + 
> > nbg_vectors , stamp_size * stamp_size );
> >
> > but this doesn't look right. Because it is a structure do I declare 
> > each bit before and after the . as a separate GSL vector? Sorry if 
> > this seems like an obvious question!
> >
> > Kind Regards,
> >
> > Matt
> >
> >
> > _______________________________________________
> > Help-gsl mailing list
> > address@hidden
> > http://lists.gnu.org/mailman/listinfo/help-gsl
> ---------------------------------------------------------
>
> Dr John Gehman (address@hidden)
> Research Fellow; Separovic Lab
> School of Chemistry
> University of Melbourne (Australia)