Product software implementation method result in ambiguity when questions arise in the execution of the implementation process. On the other hand methods can be used as a profession, meaning that the method should be taken strict and the usage of the method should be a profession, instead of a guiding principle. This view is very useful if the implementation process is very complex and is very dependent on exact and precise acting. Organizational and quality management will embrace this view, as a strict usage of any method results in more clarity on organizational level. Change management however might indicate that more flexibility in an
Quasi-Newton method He developed the first quasi-Newton algorithm in 1959: the DFP updating formula, which was later popularized by Fletcher and Powell in 1963, but is rarely used today. The most common quasi-Newton algorithms are currently the SR1 formula (for "symmetric rank-one"), the BHHH method, the widespread BFGS method (suggested independently by Broyden, Fletcher, Goldfarb, and Shanno, in 1970), and its low-memory extension L-BFGS. The Broyden's class is a linear combination of the DFP and BFGS methods. The SR1 formula does not guarantee the update matrix to maintain positive-definiteness and can be used for indefinite problems. The Broyden's method does not require