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Ublas : |
Subject: Re: [ublas] Slicing
From: Markus Weimer (mailinglists2008_at_[hidden])
Date: 2008-11-27 11:23:37
Hi Ralf and other knowledgeables,
thanks for your hint. This seems to work, but not in my case. I want
to set some elements of a row of a matrix based on the multiplication
of a one matrix with a subset of the columns of another one. Sounds a
bit complicated and it probably is:
> ublas::row(G, i) = ublas::row(ublas::prod(GF, X), j);
G and X are dense ublas::matrix<double>. I want to ignore the same
columns in G and X. However, I cannot even define an indirect array as
suggested via:
> ublas::indirect_array<ublas::matrix_row<ublas::matrix<double> > >
> g_indices;
I get the following error:
> boost/numeric/ublas/storage.hpp:1281: error: no type named
> 'const_pointer' in 'class boost::numeric::ublas::matrix_row<...>'
The same happens when I try to define the index on X. Could it be that
indices are only possible on "real" vectors as opposed to
vector_expressions?
Thanks again for your support!
Markus
> I don't think that such a "\setminus" slice is possible in ublas. If
> I understood your question correctly, then you have to set up (in a
> loop or so) an
>
> ublas::indirect_array<> relevant(len);
>
> containing the relevant indices, i.e. all those *not* belonging to
> the slice, and than use
>
> new_vec = ublas::project(vec, relevant);
>
> to get only the relevant values out of vec.
>
> At least I'm doing something similar in my code ...
>
> Ciao
>
> Ralf
>
>
>> Hi,
>>
>> I'd like to take a given vector_expression v and get one that
>> contains
>> all the entries in it, but not the ones in a range of indices. The
>> docs
>> only describe the opposite case it seems. Is it possible to
>> construct a
>> vector-slice in my case?
>>
>> Thanks in advance,
>>
>> Markus
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