Re: [eigen] Eigen with Boost::smart_ptr

[Jim Bosch <talljimbo@xxxxxxxxx>]

On 11/08/2011 08:44 AM, Christoph Hertzberg wrote:
> Hi,
>
> On 08.11.2011 13:07, Sathishkumar Duraisamy wrote:
> > Hi all,
> >
> > I am in some kind of signal processing application. To manage and
> > manipulate data, I have been using Eigen Matrix.
> >
> > Can you please give me some recommendation for using pointers for
> > dynamically allocated eigen matrix?
>
> I guess you need to be a bit more specific for that ...
> Maybe you don't need to dynamically allocate your matrices at all, since
> Eigen::MatrixXd already dynamically allocate their memory.
>
> Side note: That might actually be a nice feature, having kind-of a
> shared matrix, i.e. multiple instances of the same matrix share the same
> memory until the matrix is modified, in which case it allocates new
> memory (unless of course it is the last instance using that memory).

I've actually been working on shared Eigen matrices as part of an Eigen 
interface to another project, and I'd be happy to contribute code to 
that effect, but it's not as straightforward as one might expect.  For 
instance, when one gets a block of a shared matrix, does the block share 
memory with the original?  That would make it a lot harder for the 
compiler to optimize away the block, but it would make it a lot more 
sensible when you want to return the block from a function where the 
matrix is a local variable.

> > Is it possible to use boost::smart_ptr and boost::pointer_container
> > with Eigen Matrix. In case, which is good smart_ptr, shared_ptr or
> > week ptr?
>
> I can't see a reason why it is not possible.
>
> smart_ptr is just the name of the library, isn't it?
> W.r.t shared_ptr vs weak_ptr: you can construct weak_ptr only from
> shared_ptr, so you need at least one shared_ptr per matrix anyways.
> What's better afterwards depends on what you are planning to do.

I agree, and I'd also say that I can think of very few situations in 
which one would gain anything by using pointer container with Eigen, 
though it is possible.  Pointer container is mainly intended for holding 
hierarchies of polymorphic classes.

Jim