Schüle Daniel wrote: > Hello NG, > > given this call to roots funtion from pylab
It's actually from numpy and numpy questions are best asked (and best answered!) on numpy-discussion. http://www.scipy.org/Mailing_Lists > In [342]: roots([0,2,2]) > Out[342]: array([-1.]) > > as far as I understand it [a0,a1,a2] stands for a0+a1*x+a2*x^2 > in the above case it yields 2x^2+2x = 2x(1+x) > and the roots are 0 and -1 > I am wondering why roots function gives me only the -1 No, it's the other way around. In [1]: from numpy import * In [2]: roots? Type: function Base Class: <type 'function'> Namespace: Interactive File: /Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/numpy-1.0.2.dev3507-py2.5-macosx-10.4-i386.egg/numpy/lib/polynomial.py Definition: roots(p) Docstring: Return the roots of the polynomial coefficients in p. The values in the rank-1 array p are coefficients of a polynomial. If the length of p is n+1 then the polynomial is p[0] * x**n + p[1] * x**(n-1) + ... + p[n-1]*x + p[n] So you were really solving 2*x + 2 = 0, the single root of which is -1. > second try > > In [343]: roots([1,0,0]) > Out[343]: array([], dtype=float64) > > ok, as it should be No, that's actually wrong. What version of numpy are you using? With a recent SVN checkout of numpy, I get the correct answer: In [3]: roots([1,0,0]) Out[3]: array([ 0., 0.]) -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list