@article{727711,
      author = {Milton, K. A.,},
      url = {http://library.usi.edu/record/727711},
      title = {Schwinger's quantum action principle from Dirac's  formulation through Feynman's path integrals, the  Schwinger-Keldysh method, quantum field theory, to source  theory / [electronic resource] :},
      abstract = {Starting from the earlier notions of stationary action  principles, these tutorial notes shows how Schwinger's  Quantum Action Principle descended from Dirac's  formulation, which independently led Feynman to his  path-integral formulation of quantum mechanics. Part I  brings out in more detail the connection between the two  formulations, and applications are discussed. Then, the  Keldysh-Schwinger time-cycle method of extracting matrix  elements is described. Part II will discuss the variational  formulation of quantum electrodynamics and the development  of source theory.},
      recid = {727711},
      pages = {1 online resource (viii, 116 pages) :},
}