History of variational principles in physics involves integrals over an interval of time and (for fields) extended region of space. Moreover, in the usual formulation of classical action principles, the initial and final states of the system are fixed, e.g., In particular, the fixing of the "final" state appears to give the action principle a teleological character which has been controversial historically. This apparent teleology is eliminated in the quantum mechanical version of the action principle. History of variational principles in physics A variational principle in physics is an alternative method for determining the state or dynamics of a physical system, by identifying it as an
Letters in Mathematical Physics abstract or index "Letters in Mathematical Physics": Academic OneFile, Academic Search, Astrophysics Data System, Chemical Abstracts Service, Current Contents/Physical, Chemical and Earth Sciences, Current Index to Statistics, EBSCO, EI-Compendex, INIS Atomindex, Inspec, Mathematical Reviews, ProQuest, Science Citation Index, Scopus, Summon by Serial Solutions, and Zentralblatt MATH. According to the Journal Citation Reports, its 2011 impact factor is 1.819 and 2012 impact factor is 2.415. Letters in Mathematical Physics Letters in Mathematical Physics is a peer-reviewed scientific journal in mathematical physics published by Springer Science+Business Media. It publishes letters and longer research articles, occasionally also articles containing topical reviews. It is