Thread: [Matplotlib-users] polyfit degree problem ?

Dear All,

I have a problem using polyfit with a degree greater than 118 :

The code is :
matplotlib.mlab.polyfit(  x,  y,  pow ) # pow is degree of polynomial

for pow in range 118 and  238 the error is :
LinAlgError, 'singular martix'

and for pow greater than 237 this error raise :
OverflowError : math range error
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On Sat, May 3, 2008 at 3:11 AM, sa6113 <s.p...@gm...> wrote:
>
>  Dear All,
>
>  I have a problem using polyfit with a degree greater than 118 :
>
>  The code is :
>  matplotlib.mlab.polyfit(  x,  y,  pow ) # pow is degree of polynomial
>
>  for pow in range 118 and  238 the error is :
>  LinAlgError, 'singular martix'
>
>  and for pow greater than 237 this error raise :
>  OverflowError : math range error

matplotlib.mlab.polyfit is deprecated (and is a thin wrapper to
numpy.polyfit in the current implementation).  Please direct polyfit
questions and problems to the numpy list.

JDH

sa6113 wrote:
> Dear All,
> 
> I have a problem using polyfit with a degree greater than 118 :

The problem is that polynomial fitting generally doesn't make sense for 
degree higher than 4 or 5--if that--and at very high degree it is 
inevitable that the matrix will become singular. In other words, there 
is not enough information in the data to uniquely determine the fit. 
Whatever it is you are trying to to, fitting a polynomial with a high 
degree is the wrong way to do it.

Eric

> 
> The code is :
> matplotlib.mlab.polyfit(  x,  y,  pow ) # pow is degree of polynomial
> 
> for pow in range 118 and  238 the error is :
> LinAlgError, 'singular martix'
> 
> and for pow greater than 237 this error raise :
> OverflowError : math range error