EulerOperator

EulerOperator[0, functions][expr]
gives the action of the Euler operator or variational derivative, in respect to a given set of functions, on an expression expr.
EulerOperator[order, functions][expr]
gives the action of the higher Euler operator or Lie-Euler operator of order order, in respect to a given set of functions, on an expression expr.
  • The order can be a vector of integers with dimension equal with dimension of the variable space of the functions.
  • functions is given as a list of functions.
  • expr can be any expression including the functions and the derivatives of them.