[Numpy-discussion] matrix norm

Jason Grout jason-sage@creativetrax....
Mon Oct 22 15:09:39 CDT 2012


On 10/22/12 3:03 PM, Pauli Virtanen wrote:
> Jason Grout <jason-sage <at> creativetrax.com> writes:
> [clip]
>> I think we've established that the other software mentioned does indeed
>> use the spectral norm by default.  I'm still curious: what was the
>> reason for breaking with the norm (pun intended :)?  Any chance that in
>> a (probably far distant) future release, the norm default could be
>> changed to conform with matlab/octave/mathematica's view of the world?
>> It's not a huge deal to me now that I know to watch out for it, but it
>> did just bite me and a student a few times.
>
> The trail leads to here:
> http://projects.scipy.org/numpy/attachment/ticket/36/numpy-6-norm-change-
> default.diff
>
> Seems like the chances of learning the reason why this change was done
> are pretty slim.

Thanks for tracking this down.  It looks like the default used to be the 
spectral norm.  I guess there still is a question of if it is possible 
to change it back at this point.

FYI, in Sage, we were following the numpy convention (default  = 
Frobenius norm) for numerical matrices, but we are now switching the 
default to be the spectral norm [1].

Thanks,

Jason

[1] http://trac.sagemath.org/sage_trac/ticket/13643



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