Introduction to numerical analysis
Notes: 用高斯消元法求解时，比较计算后和计算前的主对角元，比值越小、解的精度就少多少(?) (Using double precision floating point number) 系数矩阵条件数在百亿量级（1e10）时， 解的精度大概只有1e-3或1e-4。——陈璞
Merit function for solving nonlinear equations is a scalar-valued function that indicates whether a new iterate is better or worse than the current iterate, in the sense of making progress toward a root. Merit functions are often obtained by combining the components of the vector field in some way, e.g. the sum of squares; all of which have some drawbacks.
Line search and trust-region techniques play an equally important role in optimization, but one can argue that trust-region algorithms have certain theoretical advantages in solving nonlinear equations.