Canonical Transformations

  • Walter Dittrich
  • Martin Reuter


Let q1, q2,... , q N , p1.p2,... p N be 2N independent canonical variables, which satisfy Hamilton’s equations:
$$ {\dot q_i} = \frac{{\partial H}}{{\partial {p_i}}},\;\;\;{\dot p_i} = - \frac{{\partial H}}{{\partial {p_i}}},\;\;\;i = 1,\;2,\; \ldots ,N\;{\rm{.}} $$
We now transform to a new set of 2N coordinates Q1,... Q N , P1,... P N , which can be expressed as functions of the old coordinates:
$$ {Q_i} = {Q_i}({q_i},{p_i};\;t)\;,\;\;\;{P_i} = {P_i}({q_i},{p_i};\;t)\;{\rm{.}} $$
These transformations should be invertible. The new coordinates Q i , P i are then exactly canonical if a new Hamiltonian K(Q, P, t) exists with
$$ {\dot Q_i} = \frac{{\partial K}}{{\partial {P_i}}}\;,\;\;\;\;{\dot P_i} = - \frac{{\partial K}}{{\partial {Q_i}}}\;{\rm{.}} $$
Our goal in using the transformations (4.2) is to solve a given physical problem in the new coordinates more easily. Canonical transformations are problem-independent; i.e., (Q i , P i ) is a set of canonical coordinates for all dynamical systems with the same number of degrees of freedom, e.g., for the two-dimensional oscillator and the two-dimensional Kepler problem. Strictly speaking, for fixed N, the topology of the phase space can still be different, e.g., ℝ2N, ℝ n x (S1) m , n + m = 2N etc.


Torque Librium 


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Copyright information

© Springer-Verlag Berlin Heidelberg 1992

Authors and Affiliations

  • Walter Dittrich
    • 1
  • Martin Reuter
    • 2
  1. 1.Institut für Theoretische PhysikUniversität TübingenTübingenFed. Rep. of Germany
  2. 2.Institut für Theoretische PhysikUniversität HannoverHannover 1Fed. Rep. of Germany

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