python计算函数 f(x) = 0的根，python,## module bi

python计算函数 f(x) = 0的根，python,## module bi

## 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,ceilimport errordef 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    if f1*f2 > 0.0: error.err('Root is not bracketed')    n = ceil(log(abs(x2 - x1)/tol)/log(2.0))    for i in range(n):        x3 = 0.5*(x1 + x2); f3 = f(x3)        if (switch == 1) and (abs(f3) > abs(f1)) \                         and (abs(f3) > abs(f2)):            return None           if f3 == 0.0: return x3        if f2*f3 < 0.0: x1 = x3; f1 = f3        else:           x2 = x3; f2 = f3    return (x1 + x2)/2.0