dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

Florian!

I cannot really follow your implementation of the binary addition operator. 
See

  http://www.cs.caltech.edu/courses/cs11/material/cpp/donnie/cpp-ops.html

For an extensive discussion of the subject.

But yes, the binary linear algebra operators were not implemented in C++ 
because of of performance issues. "Forcing" the user to use the compound 
assignment operators (+=, -+, *=) instead. 

Another design decision that also kicks in here is to keep it simple. We have 
many different Vector and Matrix classes, which intentionally should have 
minimalistic interface.

Occasionally we have discussed adding them, as they are there in the Python 
interface, but landed on not including them.

Johan

On Thursday June 17 2010 11:23:50 Florian Rathgeber wrote:
> Hi,
> 
> I was wondering why +=, *=, etc. are overloaded in the Vector class, but
> not addition of Vectors and multiplication of Vectors by scalars.
> 
> Hence I tried the following:
> 
> namespace dolfin
> {
>   Vector operator*( double a, const Vector& v )
>   {
>     Vector res( v );
>     res *= a;
>     return res;
>   }
> 
>   Vector operator*( const Vector& v, double a )
>   {
>     Vector res( v );
>     res *= a;
>     return res;
>   }
> 
>   Vector operator+( const Vector& v1, const Vector& v2 )
>   {
>     Vector res( v1 );
>     res += v2;
>     return res;
>   }
> }
> 
> but realized the construction of the return object is not possible since
> the copy constructor of Vector is explicit.
> 
> Is that a design decision that this is not supposed to be possible? I
> realize that creating a temporary Vector can be quite expensive.
> 
> Florian
> 
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