A variational principle is a scientific principle used within the calculus of variations, which develops general methods for finding functions which minimize or maximize the value of quantities that depend upon those functions. For example, to answer this question: "What is the shape of a chain suspended at both ends?" we can use the variational principle that the shape must minimize the gravitational potential energy.
According to Cornelius Lanczos, any physical law which can be expressed as a variational principle describes an expression which is self-adjoint. These expressions are also called Hermitian. Such an expression describes an invariant under a Hermitian transformation.
Felix Klein's Erlangen program attempted to identify such invariants under a group of transformations. In what is referred to in physics as Noether's theorem, the Poincaré group of transformations (what is now called a gauge group) for general relativity defines symmetries under a group of transformations which depend on a variational principle, or action principle.
Read more about Variational Principle: Examples
Famous quotes containing the word principle:
“Without the Constitution and the Union, we could not have attained the result; but even these, are not the primary cause of our great prosperity. There is something back of these, entwining itself more closely about the human heart. That something, is the principle of “Liberty to all”Mthe principle that clears the path for all—gives hope to all—and, by consequence, enterprize [sic], and industry to all.”
—Abraham Lincoln (1809–1865)