Python查找函数f（x）=0根的解决方法

''' root = ridder(f,a,b,tol=1.0e-9).
 Finds a root of f(x) = 0 with Ridder's method.
 The root must be bracketed in (a,b).
'''
import error
from math import sqrt
def ridder(f,a,b,tol=1.0e-9): 
 fa = f(a)
 if fa == 0.0: return a
 fb = f(b)
 if fb == 0.0: return b
 if fa*fb > 0.0: error.err('Root is not bracketed')
 for i in range(30):
 # Compute the improved root x from Ridder's formula
 c = 0.5*(a + b); fc = f(c)
 s = sqrt(fc**2 - fa*fb)
 if s == 0.0: return None
 dx = (c - a)*fc/s
 if (fa - fb) < 0.0: dx = -dx
 x = c + dx; fx = f(x)
 # Test for convergence
 if i > 0:
 if abs(x - xOld) < tol*max(abs(x),1.0): return x
 xOld = x
 # Re-bracket the root as tightly as possible
 if fc*fx > 0.0:
 if fa*fx < 0.0: b = x; fb = fx
 else: a = x; fa = fx
 else:
 a = c; b = x; fa = fc; fb = fx
 return None
 print 'Too many iterations'