[SciPy-dev] Matlab io bug; request for advice

Gregor Thalhammer gregor.thalhammer@gmail....
Thu Feb 19 12:45:40 CST 2009


Matthew Brett schrieb:
> Hi,
>
>   
>>> Therefore I am convinced that a 1d vector
>>> in numpy (a row vector) corresponds more naturally to a column vector in
>>> matlab. I see the argument that [1:12] in matlab is a row vector, but I
>>> think this is simply to be consistent with the direct entry of matrices
>>> ([1:12; 1:12] is a 2x12 matrix) and to be more economic in displaying on
>>> screen. In my opinion this is not sufficient to deduce what should be
>>> the default shape of a 1d vector in matlab.
>>>       
>> Also, I believe matlab is inconsistent on this point anyway -- isn't
>> A(:) (basically ".ravel()") a column vector?
>>     
>
> I agree it's not completely clear what matlab thinks.
>
> However, at the moment we have:
>
> In [19]: arr = np.arange(5)
>
> In [20]: arr.shape
> Out[20]: (5,)
>
> In [21]: np.atleast_2d(arr).shape
> Out[21]: (1, 5)
>
> In [22]: scipy.io.savemat('afile.mat', {'arr':arr})
>
> In [24]: vars = scipy.io.loadmat('afile.mat')
>
> In [25]: vars['arr'].shape
> Out[25]: (5, 1)
>
> I think that is moderately surprising.
>   

Why not converting matlab 1xN or Nx1 arrays to numpy 1d arrays when 
loading from a matlab file? (If I remember correctly, this has been the 
case long time ago, at least in some of the predecessors of scipy.io). I 
guess this change would create more protest, at least on this list, 
since it would break python code instead of matlab code.

Gregor


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