Re: [eigen] On lazy evaluation and temporary matrices

[Gael Guennebaud <gael.guennebaud@xxxxxxxxx>]

Hi,

first make sure to test it in "debug mode", i.e., without NDEBUG or
EIGEN_DEBUG defined to enable the detection of some some alignment
issues. If that does not help, try to disable vectorization by
defining EIGEN_DONT_VECTORIZE.

Is your code multithreaded?

Also in your case the .eval() is superfluous.

gael

On Thu, Nov 25, 2010 at 2:45 AM, Jose Luis Blanco
<joseluisblancoc@xxxxxxxxx> wrote:
> Hi Thomas,
>
> Thanks, I added the EIGEN_ALIGN16 macro to all the number arrays, it
> definitively makes sense... but it behaves exactly the same :-(
>
> Best,
> JL
>
> PS: And yes, it's beta3*, actually an hg checkout from a few days ago...
>
> On Thu, Nov 25, 2010 at 2:22 AM, Thomas Capricelli
> <orzel@xxxxxxxxxxxxxxx> wrote:
>> It looks like an alignement problem. You should ensure "numbers" is aligned,
>> see bottom of http://eigen.tuxfamily.org/dox-devel/
>>
>> (I assume you use the devel branch.. 3.0beta*)
>>
>> regards,
>>
>> --
>>
>> Thomas Capricelli <orzel@xxxxxxxxxxxxxxx>
>>
>> http://www.freehackers.org/thomas
>>
>> On Thursday 25 November 2010 02:01:48 Jose Luis Blanco wrote:
>>
>>> Hi guys,
>>
>>>
>>
>>> I need the help of someone knowing the inner workings of Eigen. I've
>>
>>> spent a few days stuck debugging an error in some silly computations
>>
>>> with Eigen matrices, and want to rule out potential errors...
>>
>>> Consider this code:
>>
>>>
>>
>>> ======================
>>
>>> void func( Matrix<...> &m_out )
>>
>>> {
>>
>>> Matrix<...> I = ....
>>
>>> const double numbers[] = { 1.0, x(), -y()*x() , whatever, .... };
>>
>>> m_out = I * Matrix<...>(numbers);
>>
>>> }
>>
>>>
>>
>>> int main()
>>
>>> {
>>
>>> Matrix<...> M;
>>
>>> func(M);
>>
>>> cout << M << endl;
>>
>>> }
>>
>>> ======================
>>
>>>
>>
>>> Is it a problem for the temporary object "Matrix<...>(numbers)" to be
>>
>>> created with a pointer to memory on the stack, while the evaluation of
>>
>>> the object for the matrix product is actually evaluated *out* of that
>>
>>> function (where obviously that pointer is invalid)??
>>
>>>
>>
>>> I ask because I'm having a very erratic behavior in code like above
>>
>>> (on GCC doesn't work, it does on MSVC; adding a "cout << ..." for an
>>
>>> unrelated matrix changes the result, etc...).
>>
>>> Is it necessary to use instead:
>>
>>>
>>
>>> ( I * Matrix<...>(numbers) ).eval();
>>
>>>
>>
>>> or not even with this .eval() is my code correct?
>>
>>> I'm still having random wrong matrix elements with and without eval(),
>>
>>> so I wanted to be sure on this part before keep on debugging...
>>
>>>
>>
>>> Thanks for your time!
>>
>>> JL
>>
>>>
>>
>>>
>>
>>>
>
>
>
> --
> ___________________________________________________________
>
> Dr. Jose-Luis Blanco-Claraco
> Dpt. Ing. Civil, Mat. y Fabric - Phone: +34 952 152435
> E.T.S.I. Industriales - Despacho 2.037
> Dpt. Ing. Sist. y Automática  - Phone: +34 952 132848
> E.T.S.I. Telecomunicacion - Lab. 2.3.6
> Universidad de Malaga - Campus Universitario de Teatinos
> 29071 Malaga, Spain
> http://www.isa.uma.es/jlblanco
> http://www.mrpt.org/
> ___________________________________________________________
>
>
>