Re: [boost] Re: ublas: reserve

From: Toon Knapen (toon.knapen_at_[hidden])
Date: 2001-12-10 10:59:11

jhrwalter wrote:

> --- In boost_at_y..., Toon Knapen <toon.knapen_at_s...> wrote:
> 
>>>This is indeed an alternative. matrix_range should be an suited 
>>>submatrix adaptor (with a poor name?). 
>>>
>>
>> > [and in another thread]
>> > matrix_range is well suited to address a sub matrix of an 
>>
> existing
> 
>> > matrix. But one has to consider carefully, what code a compiler 
>>
> emits
> 
>> > with this additional indirection, AFAIK
>>
>>
>>but matrix_range does not feature a resize(size_type,size_type).
>>The idea would be that you can constantly resize the adaptor 
>>(matrix_range) as long as it is smaller or equal in size to the 
>>
> matrix 
> 
>>it originates from.
>>
>  
> I usually construct a new adaptor, for example:
>  
> matrix<double> m (size, size);
> for (int i = 0; i < size; ++ i) {
>     matrix_range<matrix<double> > mr (m, range (0, i), range (0, i));
>     ...
> }

OK. (maybe a real resize might be faster although it's better to first 
prove that there is a performance diff, 'early optimisation is the root 
of all evil ;-)

> 
> 
>> > [and yet in another thread]
>> > Correct. matrix_range checks it's dimensions against the 
>>
> dimensions
> 
>> > of the underlying matrix.
>>I can't find that, the constructors e.g. looks like :
>>
>>  NUMERICS_INLINE
>>  matrix_range (matrix_type &data, const range &r1, const range 
>>
> &r2):
> 
>>     data_ (data), r1_ (r1), r2_ (r2) {}
>>
>  
> Oops. The checks are deferred until element access or iterator 
> dereference. Is that too late?

can't find the check there either (I just ask because I'm trying to 
understand all sources)
e.g. :
in matrix_range class

         NUMERICS_INLINE
         reference_type operator () (size_type i, size_type j) {
             return data_ (r1_ (i), r2_ (j));
         }

no check here ?