Complex sentence: In optimization, quasi-Newton methods are well-known algorithms for finding local maxima and minima of functions, just like Newton's method, but quasi-Newton methods approximate the inverse Hessian matrix in order to reduce the amount of computation per iteration.
Split into simpler sentences: In optimization, quasi-Newton methods are well-known algorithms for finding local maxima and minima of functions. Quasi-Newton methods are based on Newton's method, but they approximate the inverse Hessian matrix in order to reduce the amount of computation per iteration.