[Dune] MultiLinearGeometry

[Martin Nolte]

Hi Oli,

first of all, I'm not an expert on the stl, so there might be a way to put the 
reference counter into the object the smart pointer points to. However, as far 
as I understand things, the shared_ptr actually points to a control structure 
containing (at least) the following:
- a counter of strong references (by shared_ptr),
- a counter of weak references (by weak_ptr),
- a pointer to the real object in memory.
Unfortunately, this control structure must be allocated somehow, so there is an 
additional "new" (again, there might be a way around this that I don't know of). 
Moreover, dereferencing a shared_ptr either dereferences two pointers (the one 
to the control structure and the pointer to the real object), or the 
shared_pointer needs to contain both pointers.

In summary: The shared_ptr seems unnecessarily expensive to me if I just want a 
simple reference counting pointer (being prepared to store the reference count 
on the object itself).

Puh, a long answer. Maybe someone more into the stl can enlighten me on where 
I'm right and where I'm wrong. Until then, I prefer coding it myself ;-).

Best,

Martin

On 10/12/2012 05:11 PM, Oliver Sander wrote:
> Hi Martin,
>
>> as the name says, the user data field is for your data. GeometryGrid
>> uses it for the reference count.
>
> just out of curiosity: what's wrong with the stl way of reference counting?
>
> best,
> Oliver
>
>> If you specify an empty class, no
>> memory is used (a trick I learned from gcc's std::vector). If you don't
>> need it, just leave it at the default (empty).
>>
>> Best,
>>
>> Martin
>>
>> On 10/12/2012 04:50 PM, Oliver Sander wrote:
>>> Hi Martin,
>>> thanks! I'm looking forward to making UGGrid use that instead of
>>> BasicGeometry.
>>> Can you give a short explanation what the userData is good for?
>>> best,
>>> Oliver
>>>
>>> Am 12.10.2012 16:03, schrieb mnolte at dune-project.org:
>>>> Author: mnolte
>>>> Date: 2012-10-12 16:03:14 +0200 (Fri, 12 Oct 2012)
>>>> New Revision: 1072
>>>>
>>>> Modified:
>>>> recent_changes.wml
>>>> Log:
>>>> announce the new MultiLinearGeometry (see FS#1182)
>>>>
>>>>
>>>> Modified: recent_changes.wml
>>>> ===================================================================
>>>> --- recent_changes.wml 2012-10-09 16:18:26 UTC (rev 1071)
>>>> +++ recent_changes.wml 2012-10-12 14:03:14 UTC (rev 1072)
>>>> @@ -54,6 +54,11 @@
>>>> dimension and codimension. Since such hypercubes have a lot of
>>>> structure, the
>>>> implementation
>>>> is very fast.
>>>> </li>
>>>> +<li>A reimplementation of the generic geometries,
>>>> named<kbd>MultiLinearGeometry</kbd>
>>>> + has been added. It comes without a complicated TMP and abandons the
>>>> use of
>>>> dynamic
>>>> + polymorphism in the case of multiple geometry types. Despite these
>>>> simplifications,
>>>> + it shows slightly better performance.
>>>> +</li>
>>>> </ul>
>>>>
>>>> <h3>Deprecated and removed features</h3>
>>>> @@ -91,6 +96,9 @@
>>>> Jacobians to be FieldMatrices anymore. The precise interface
>>>> requirements for
>>>> these matrices
>>>> is still being worked out.
>>>> </li>
>>>> +<li><kbd>GeometryGrid</kbd> now uses the
>>>> new<kbd>MultiLinearGeometry<kbd>
>>>> instead of the
>>>> + generic geometry implementaton.
>>>> +</li>
>>>> </ul>
>>>>
>>>> <h3>Deprecated and removed features</h3>
>>>>
>>>>
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-- 
Dr. Martin Nolte <nolte at mathematik.uni-freiburg.de>

Universität Freiburg                                   phone: +49-761-203-5630
Abteilung für angewandte Mathematik                    fax:   +49-761-203-5632
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79104 Freiburg, Germany