Polyfit is returning coefficients from low to high instead of high to low.

Docs say that np.polyfit returns:

Polynomial coefficients, highest power first. If y was 2-D, the coefficients for k-th data set are in p[:,k].

However, at least for the linear case, it is actually returning coefficients lowest power first. Thus, for a fit y=mx+b, polyfit returns (b,m) and not (m,b) as the docs indicate.

y=np.linspace(0,10,10) 
x=y

plt.plot(x,y)
m,b=polyfit(x,y,1)  #Returns highest power first
print 'm is', m, 'b is', b

Output gives:

m is 0.0 b is 1.0

See that it’s reversed?

[charris]

There are two polyfits, are you by chance using the one in numpy.polynomial.polynomial.

[hugadams]

Yes thanks On Mar 8, 2013 7:29 PM, “Charles Harris” [e-mail] wrote:

Seems settled.

— Reply to this email directly or view it on GitHubhttps://github.com/numpy/numpy/issues/3119#issuecomment-14654012 .