[SciPy-dev] pbm in numpy.linalg.polyfit and nupy.linalg polyfit

[Stéfan van der Walt]

Hi Julien

Would you mind filing a bug at

http://projects.scipy.org/scipy/numpy

so that we don't lose track of this issue?

Thanks
Stéfan

On Wed, Mar 12, 2008 at 8:58 PM, Julien Le Sommer <lesommer at hmg.inpg.fr> wrote:
>
> Hi,
>
> I just want to mention  a possible bug in numpy/lib/polynomial.py
> with numpy version > 1.0.4 (with python2.4).
>
> the modification introduced with revision 3338 of numpy by charris,
> (see http://www.scipy.org/scipy/numpy/log/trunk/numpy/lib/polynomial.py)
>  has broken the possibility to use polyfit with two-dimensional arrays.
>
> IPython gives the following message :
> ------------------------------------------------------------------------------------------
>     308     # scale returned coefficients
>      309     if scale != 0 :
> --> 310         c /= vander([scale], order)[0]
>     311
>     312     if full :
>
> ValueError: shape mismatch: objects cannot be broadcast to a single shape
> --------------------------------------------------------------------------------------------
>
> with the following script :
> --------------------------------------------------------------------------------------------
> import numpy
> from numpy.random import *
> from numpy import linalg
>
> #- create some arrays :
>  n = 100
> r = 0.5
> a = 1.4
>
> # 1D vector
> T = numpy.array(xrange(n),dtype=numpy.float32)*2/(n-1) -1.
> X = a*T +r*(rand(n)-0.5)
>
> # (n * 2) array
> aa = numpy.array([[0.7,1.2]])
> rr = numpy.array([[0.4,0.6]])
>  TT = T.reshape((n,1))*numpy.ones((n,2))
> XX = aa*TT +rr*(randn(n,2)-0.5)
>
> # (n * 3) array
> aaa = numpy.array([[0.7,1.2,1.]])
> rrr = numpy.array([[0.4,0.6,0.2]])
> TTT = T.reshape((n,1))*numpy.ones((n,3))
> XXX = aaa*TTT +rrr*(randn(n,3)-0.5)
>
>
> #- try numpy.polyfit
>
>
> # works ok
> (ar,br) = numpy.polyfit(T,X,1)
>
> # works ok
> (ar,br) = numpy.polyfit(T,XX,1)
>
> # fails
> (ar,br) = numpy.polyfit(T,XXX,1)
>
>
> --
>    Julien Le Sommer, LEGI/MEOM,
>     BP53, 38041 Grenoble cedex 9, France
>    Tel : +33 4 76 82 50 65
>    Fax : +33 4 76 82 52 71
>    http://www.legi.hmg.inpg.fr/~lesommer/
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>