[mlpack] why is ARMA_64BIT_WORD disabled ?

[Ryan Curtin]

On Fri, Apr 24, 2015 at 05:17:50PM +0200, Julien Dorval wrote:
> Hello everyone,
> 
> I am completely new in the MLPACK community, I'm trying to get it to
> work for the moment, I'm particularly interested in the EMST. I
> tried a bit by myself, but I'd rather ask competent people instead
> of breaking things on my own. I managed to get cmake what it wanted,
> but the compilation stops at:
> 
>    dorval at zoidberg:~/peoples_codes/mlpack/mlpack-master/build: make
>    ...
>    _/usr/include/armadillo_bits/compiler_setup.hpp:191:111: note:
>    #pragma message: WARNING: compiler is in C++11 mode, but it has
>    incomplete support for C++11 features;__
>    __/usr/include/armadillo_bits/compiler_setup.hpp:192:86: note:
>    #pragma message: WARNING: if something breaks, you get to keep all
>    the pieces__
>    __/usr/include/armadillo_bits/compiler_setup.hpp:193:93: note:
>    #pragma message: WARNING: To forcefully prevent Armadillo from using
>    C++11 features,__
>    __/usr/include/armadillo_bits/compiler_setup.hpp:194:90: note:
>    #pragma message: WARNING: #define ARMA_DONT_USE_CXX11 before
>    #include <armadillo>_
>    ...

Hi Julien,

What compiler are you using?  Is it possible that you could use a newer
compiler with C++11 support?  Also, what was the CMake output?  Did it
say "Checking for C++11 compiler - unavailable" and continue anyway?

The error you get, even after defining ARMA_DONT_USE_CXX11, is a C++11
related error:

>    /home/dorval/peoples_codes/mlpack/mlpack-master/src/mlpack/core/dists/discrete_distribution.cpp:7:
>    /home/dorval/peoples_codes/mlpack/mlpack-master/src/mlpack/../mlpack/core/dists/gaussian_distribution.hpp:34:42:
>    erreur: both ‘const’ and ‘constexpr’ cannot be used here
>    make[3]: ***
>    [src/mlpack/CMakeFiles/mlpack.dir/core/dists/discrete_distribution.cpp.o]
>    Erreur 1
>    make[2]: *** [src/mlpack/CMakeFiles/mlpack.dir/all] Erreur 2
>    make[1]: *** [src/mlpack/methods/emst/CMakeFiles/emst.dir/rule] Erreur 2
>    make: *** [emst] Erreur 2

The master branch of mlpack does require a C++11 compiler, but, older
versions (1.0.12 or older) can use a regular C++03 compiler.  So maybe
you should try downloading an older version of mlpack, and an older
version of Armadillo.  The emst code should run at about the same speed.

> Ok, so I tried to solve this myself by adding
> 
>    #define ARMA_DONT_USE_CXX11
> 
> before :
> 
>    #include <armadillo>
> 
> 
> In build/include/mlpack/core/arma_extend/arma_extend.hpp  and
> src/mlpack/core/arma_extend/arma_extend.hpp
> 
> 
> Now the compilation does this:
> 
>    ...
>    note: #pragma message: mlpack was compiled with ARMA_64BIT_WORD, but
>    you are compiling wit
>    hout ARMA_64BIT_WORD.  This will almost certainly cause irreparable
>    disaster.  Either enable ARMA_64BIT_WORD in your application which
>    is using mlpack, or, recompile mlpack against a version of Arma
>    dillo which has ARMA_64BIT_WORD disabled.
>    ...
> 
> I'm using armadillo 5.0 which I understand has ARMA_64BIT_WORD
> enabled by default. Why wasn't MLPACK compiled with ARMA_64BIT_WORD
> ? Am I not actually compiling mlpack right now ?

So, this message is actually a red herring.  I wrote some CMake scripts
which check for ARMA_64BIT_WORD in Armadillo and then ensure that the
same setting is enabled for the compilation of the mlpack library.  But
these scripts count on ARMA_DONT_USE_CXX11 being defined -- which it
isn't for libmlpack.so, except for the modification that you made.  In
this particular case, I *think* you can ignore this warning because of
the change you made, but I really think your best bet is getting a new
compiler.

In the case that a new compiler is out of the question (i.e. if you're
on a departmental system and the IT team moves slower than molasses,
etc.), probably pairing mlpack 1.0.12 with Armadillo 3 or 4 should give
you working results.  I think.

I hope this is helpful -- please let me know if I can clarify anything
further.

Thanks,

Ryan

-- 
Ryan Curtin    | "If it's something that can be stopped, then just try to stop it!"
ryan at ratml.org |   - Skull Kid