Brent的zeroin算法，快速求解非线性方程的根。 来源 http://people.sc.fsu.edu/~jburkardt/c_src/brent/brent.html(Brent's zeroin algorithm is used to quickly solve the roots of nonlinear equations. From http://people.sc.fsu.edu/~jburkardt/c_src/brent/brent.html)