Re: [ublas] size_type for mapped_matrix

Subject: Re: [ublas] size_type for mapped_matrix
From: Alex Hagen-Zanker (ahh34_at_[hidden])
Date: 2011-04-13 17:20:57

Dear Jörn,

.
  On 13/04/2011 18:19, Ungermann, Jörn wrote:
> Hi,
>
> I think you are right in your observation that mapped_matrix is not consistent there.
>
> Do you really have a sparse matrix with more than 2^32 non-zero entries? That would imply that you have about one third of non-zeros. I am not sure that a sparse approach is then still the most efficient one.
>
  I do not have that many non-zero entries. The matrix dimensions are 
120 000 * 120 000 but the number of non-zero entries is about 60000.

The problem is not the number of entries a std::map can hold, but the 
size of the indices themselves. I can provide a std::map that uses long 
unsigned int as the key, but internally mapped_matrix sticks with size_t 
and hence produces wrong results.

> However, I'd use coordinate_matrix for construction, as inserting elements is *much* cheaper than for mapped_matrix, especially if you have more than 2^32 entries.
>
> ublas::coordinate_matrix<double, ublas::row_major, 0, ublas::unbounded_array<long unsigned int, MyAllocator>
>        >  MyTypeName;
>
> You still have the problem then that unbounded_array uses size_t internally to manage the memory, which will probably a problem for you? The only way around *that* is writing your own allocator (MyAllocator above), as std::allocator also uses size_t.
Your suggestion of using a coordinate matrix works very well, except for 
a large amount of warnings about casts of long int to size_t that I ignore.

Thanks for your help, Alex

>> -----Original Message-----
>> From: ublas-bounces_at_[hidden] [mailto:ublas-
>> bounces_at_[hidden]] On Behalf Of Alex Hagen-Zanker
>> Sent: Mittwoch, 13. April 2011 11:08
>> To: ublas_at_[hidden]
>> Subject: [ublas] size_type for mapped_matrix
>>
>> Dear All,
>>
>> I am using a mapped_matrix as a sparse matrix for a matrix with
>> dimensions 120 000 * 120 000. As this exceeds the limits of size_t I
>> thought to step away from the default template parameters and use:
>>
>>       mapped_matrix<double, row_major, map_std<long long, double>  >
>> myMatrix
>>
>> This does not solve my problem as the mapped_matrix::size_type is still
>> size_t. Looking at the ublas source code I see that
>> mapped_matrix::size_type boils down to std::map<long long,
>> double>::size_type.
>>
>> It seems to me that this should be std::map<long long,
>> double>::key_type
>> instead.
>>
>> Is this a bug, or am I expecting too much?
>>
>> Can I use one of the other sparse matrix types instead?
>>
>> Thanks, Alex
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>> ublas mailing list
>> ublas_at_[hidden]
>> http://lists.boost.org/mailman/listinfo.cgi/ublas
>> Sent to: j.ungermann_at_[hidden]
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-- 
Alex Hagen-Zanker
University of Cambridge, Department of Architecture,  1-5 Scroope Terrace, Cambridge, CB2 1PX, United Kingdom
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