Re: [Matplotlib-users] Bug in polyfit/polyval

[Stephen W. <ste...@cs...>]

kristen kaasbjerg wrote:

>Hola
>
>When i try to fit a polynomial of order 4 to 5 data
>points, I get an answer far from what I would expect.
>  
>
If I run your script and print out the polynomial coefficients, they are 
very large and alternate in sign:

In [166]: p
Out[166]:
array([ -1779.1645838 ,   7613.24170642, -12137.79572888,
         8529.6429996 ,  -2239.34146635])

This means that the problem is ill posed.  In general, high order 
polynomial fitting is a bad idea;  if you just want an interpolant and 
don't care about coefficients, use a cubic spline.