python計算函數 f(x) = 0的根的代碼

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## module bisection
''' root = bisection(f,x1,x2,switch=0,tol=1.0e-9). Finds a root of f(x) = 0 by bisection. The root must be bracketed in (x1,x2). Setting switch = 1 returns root = None if f(x) increases upon bisection. '''    
from math import log,ceil
import error
 
def bisection(f,x1,x2,switch=1,tol=1.0e-9):
    f1 = f(x1)
    if f1 == 0.0: return x1
    f2 = f(x2)
    if f2 == 0.0: return x2
    n = ceil(log(abs(x2 - x1)/tol)/log(2.0))
    for i in range(n):
        if (switch == 1) and (abs(f3) > abs(f1)) 
                         and (abs(f3) > abs(f2)):
            return None   
        if f3 == 0.0: return x3
        else:           x2 = x3; f2 = f3
    return (x1 + x2)/2.0              複製代碼