# Applications of Lie Groups to Differential Equations by Peter J. Olver By Peter J. Olver

This booklet is dedicated to explaining quite a lot of purposes of con­tinuous symmetry teams to bodily very important platforms of differential equations. Emphasis is put on major purposes of group-theoretic tools, geared up in order that the utilized reader can quite simply study the elemental computational thoughts required for actual actual difficulties. the 1st bankruptcy collects jointly (but doesn't end up) these points of Lie staff idea that are of significance to differential equations. purposes lined within the physique of the e-book comprise calculation of symmetry teams of differential equations, integration of standard differential equations, together with specified strategies for Euler-Lagrange equations or Hamiltonian platforms, differential invariants and building of equations with pre­scribed symmetry teams, group-invariant strategies of partial differential equations, dimensional research, and the connections among conservation legislation and symmetry teams. Generalizations of the elemental symmetry crew thought, and purposes to conservation legislation, integrability stipulations, thoroughly integrable platforms and soliton equations, and bi-Hamiltonian platforms are lined intimately. The exposition in all fairness self-contained, and supplemented by means of various examples of direct actual significance, selected from classical mechanics, fluid mechanics, elasticity and different utilized components.

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Extra resources for Applications of Lie Groups to Differential Equations (Graduate Texts in Mathematics, Volume 107)

Example text

Maps Between Manifolds If M and N are smooth manifolds, a map F: M -+ N is said to be smooth if its local coordinate expression is a smooth map in every coordinate chart. e. on the subset Xa[ Va n F- 1 ( U/3)]). In other words, a smooth map is of the form y = F(x), where F is a smooth function on the open subsets giving local coordinates x on M and y on N. 5. An easy example is given by the map f: IR-+ S\ f(t) = (cos t, sin t). In terms of the angular coordinate 8 on S\ f is a linear function: 8 = t mod 27T, and so is clearly smooth.

As a manifold T(n) can be identified with the Euclidean space IR n (n-1)/2 since each matrix is uniquely determined by its entries above the diagonal. For instance, in the case of T(3), we identify the matrix ( 1 o x 1 °0 Z) Y E T(3) 1 with the vector (x, y, z) in 1R3. However, except in the special case of T(2), T(n) is not isomorphic to the abelian Lie group IR n(n-i)/2. In the case of T(3), the group operation is given by (x, y, z) . (x', y', z') = (x+x', y+ y', z+ z'+xy'), using the above identification.

Often, as computations are most easily done in local coordinates, the choice of a special coordinate chart in which the object of interest takes a particularly simple form will enable us to considerably simplify many of these computations. The use of this basic technique will become clearer as we continue. Often one expands the collection of coordinate charts to include all those compatible with the defining charts. ). The easy details of proving that two charts, compatible with the defining charts, are mutually compatible, are left to the reader.