Introduction to Numerical Methods for Variational Problems
  MLA
  Langtangen, and Kent-Andre Mardal. Introduction to Numerical Methods for Variational Problems. Springer International Publishing, 2019.
  APA
  Langtangen, L., & Mardal, K. (2019). Introduction to Numerical Methods for Variational Problems. Springer International Publishing.
  Chicago
  Langtangen, and Kent-Andre Mardal. Introduction to Numerical Methods for Variational Problems. : Springer International Publishing, 2019.