dolfin team mailing list archive

[Ola Skavhaug <skavhaug@xxxxxxxxx>]

Dag Lindbo skrev den 09/04-2008 følgende:
> Dag Lindbo wrote:
>> Ola Skavhaug wrote:
>>> Dag Lindbo skrev den 09/04-2008 følgende:
>>>> Hello again!
>>>>
>>>> Why is it not possible any longer to get the Vector associated with 
>>>> a Function? E.g:
>>>>
>>>> #include <dolfin.h>
>>>> using namespace dolfin;
>>>>
>>>> int main()
>>>> {
>>>>    Function u;
>>>>    Vector& v = u.vector();
>>>> }
>>>
>>> int main()
>>> {
>>>      Function u;
>>>      Vector v;
>>>      v = u.vector();
>>>      return 0;
>>> }
>>>
>>> Should work. A Function returns a GenericVector reference, and the Vector
>>> reference needs to be a Vector. Then the operator= in Vector is  
>>> applied in the
>>> assignment.
>>>
>>> Ola
>>
>> Ola,
>>
>> Sorry if I'm this is a stupid/incorrect observation. What you propose 
>> is a a deep copy of the vector. So something like
>>
>> uBlasVector& vv = *(v.instance());
>> vv[0] = 1000.32;
>>
>> has no impact on the data owned by u. uBlas only has deep copy  
>> semantics, which are invoked in dolfin::Vector::operator= (i.e. *vector 
>> = *x; )
>>
>> Is this really what we want?
>>
>> /Dag
>>
>
> Seems I'm also sloppy with grammar today. My previous post may sound  
> offensive towards Ola, but I only meant to pre-excuse _myself_ in case  
> my understanding of C++ has deserted me this evening. /Dag

No offence taken :) My point was simply that since the underlying
GenericVector is not a Vector, the lines:

Function u;
Vector& v = u.vector();

does not work. But the compiler told you that already. Do you want a method
for rebinding the DefaultVector* vector attribute of Vector? That way, the
deep copy will be avoided.

Ola

>>>  
>>>> error: invalid initialization of reference of type 
>>>> ‘dolfin::Vector&’ from expression of type ‘dolfin::GenericVector’
>>>>
>>>> na55:cpp > scons
>>>> c++ -o test.o -c -Wall -pipe -ansi -g -Werror -O2 -pthread -DDEBUG  
>>>> -DNDEBUG -DPACKAGE_VERSION="0.7.2" -DHAS_UMFPACK=1 -DHAS_GTS=1  
>>>> -I/usr/local/include  
>>>> -I/usr/lib/python2.5/site-packages/numpy/core/include  
>>>> -I/usr/include/suitesparse -I/usr/include/python2.5  
>>>> -I/usr/include/libxml2 -I/usr/include/glib-2.0  
>>>> -I/usr/lib/glib-2.0/include test.cpp
>>>> test.cpp: In function ‘int main()’:
>>>> test.cpp:8: error: invalid initialization of reference of type  
>>>> ‘dolfin::Vector&’ from expression of type ‘dolfin::GenericVector’
>>>> cc1plus: warnings being treated as errors
>>>> test.cpp:8: warning: unused variable ‘v’
>>>> scons: *** [test.o] Error 1
>>>>
>>>> I hope this functionality hasn't been removed.
>>>>
>>>> /Dag
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