[Numpy-discussion] Bug in ndarray.argmax

[Pau Gargallo]

On 5/1/06, Pierre Barbier de Reuille <p.barbier-de-reuille at uea.ac.uk> wrote:
> Hello,
>
> I notices a bug in ndarray.argmax which prevent from getting the argmax
> from any axis but the last one.
> I join a patch to correct this.
> Also, here is a small python code to test the behaviour of argmax I
> implemented :
>
> ==8<====8<====8<====8<====8<====8<====8<====8<===8<===
>
> from numpy import array, random, all
>
> a = random.normal( 0, 1, ( 4,5,6,7,8 ) )
> for i in xrange( a.ndim ):
>   amax = a.max( i )
>   aargmax = a.argmax( i )
>   axes = range( a.ndim )
>   axes.remove( i )
>   assert all( amax == aargmax.choose( *a.transpose( i, *axes ) ) )
>
> ==8<====8<====8<====8<====8<====8<====8<====8<===8<===
>
> Pierre
>
>
> diff numpy-0.9.6/numpy/core/src/multiarraymodule.c numpy-0.9.6.mod/numpy/core/src/multiarraymodule.c
> 1952a1953,1955
> >    If orign > ap->nd, then we cannot "swap it back"
> >    as the dimension does not exist anymore. It means
> >    the axis must be put back at the end of the array.
> 1956c1959,1979
> <                       (op) = (PyAO *)PyArray_SwapAxes((ap), axis, orign); \
> ---
> >                       int nb_dims = (ap)->nd;                         \
> >                       if (orign > nb_dims-1 ) {                       \
> >                               PyArray_Dims dims;                      \
> >                               int i;                                  \
> >                               dims.ptr = ( intp* )malloc( sizeof( intp )*nb_dims );\
> >                               dims.len = nb_dims;                     \
> >                               for(i = 0 ; i < axis ; ++i)             \
> >                               {                                       \
> >                                       dims.ptr[i] = i;                \
> >                               }                                       \
> >                               for(i = axis ; i < nb_dims-1 ; ++i)     \
> >                               {                                       \
> >                                       dims.ptr[i] = i+1;              \
> >                               }                                       \
> >                               dims.ptr[nb_dims-1] = axis;             \
> >                               (op) = (PyAO *)PyArray_Transpose((ap), &dims ); \
> >                       }                                               \
> >                       else                                            \
> >                       {                                               \
> >                               (op) = (PyAO *)PyArray_SwapAxes((ap), axis, orign); \
> >                       }                                               \
>
>
>

The bug seems to be still there in the current svn version, so I
filled out a ticket for this.

Is the first time i do such a thing, so someone competent should
_please_ take a look at it.

Thanks, and sorry in advance if i did something wrong.
pau