Find a root of a function in a given range

Question

I have a set of functions f_t with several roots (two actually). I want to find the \"first\" root and doing this with fsolve works fine most of th

Answer 1

Classically, you could use root:

import numpy as np
from scipy.optimize import root

def func(x, t):
    return x ** 2 - 1. / t

t = 5000

res = root(func, 0.5, args=(t, )).x[0]
print res

That would print the positive one, in this case 0.0141421356237.

If you want to specify the range and determine all roots within this interval, you can use chebpy:

from chebpy import chebfun

x = chebfun('x', [-100000, 100000])
t = 5000
f = x ** 2 - 1. / t

rts = f.roots()
print rts

This would print both the positive and the negative root, in this case

[-0.01413648  0.01413648]

If you only want to look in the positive range, you can change

x = chebfun('x', [-100000, 100000])

to

x = chebfun('x', [0, 100000])

I am, however, not sure how to use infinity, but you can just use a very high number for practical purposes, I think.