About the basics of Poisson bracket

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Discussion Overview

The discussion revolves around the properties and definitions of Poisson brackets in the context of differential geometry, specifically focusing on their well-defined nature, antisymmetry, bilinearity, and the Jacobi identity. The scope includes theoretical aspects and mathematical reasoning related to smooth functions on manifolds.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant presents a problem set regarding the Poisson bracket, asking for help to show its well-defined nature and various properties.
  • Another participant suggests that the solution involves calculating the Poisson bracket on overlapping coordinate patches and applying transformation rules for smooth functions.
  • A request for references is made to support understanding of transformation rules related to the Poisson bracket.
  • A later reply indicates that basic knowledge of smooth functions on manifolds is necessary for tackling Poisson brackets, implying that the original poster may need to review foundational concepts.

Areas of Agreement / Disagreement

The discussion does not reach a consensus, as participants express differing levels of familiarity with the foundational concepts necessary for understanding Poisson brackets. There is also a lack of agreement on the sufficiency of the original poster's background knowledge.

Contextual Notes

Limitations include potential gaps in the original poster's understanding of smooth functions on manifolds, which may affect their ability to engage with the problem effectively. The discussion also assumes familiarity with transformation rules in differential geometry.

Who May Find This Useful

Readers interested in differential geometry, mathematical physics, or those studying Poisson brackets and their properties may find this discussion relevant.

sarason
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Dear all,
Please help me to solve the following problems
about Poisson brackets.
Let M be a 2n-manifold and w is a closed non-degenerate di®eren-
tial 2-form. (Locally we write w = w_ij dx^i ^ dx^j with [w_ij ] being a
non-degenerate anti-symmetric real matrix-valued local function on M)
Let f, g be two smooth functions on M. Define the Poisson bracket
{f, g} as follows: locally,
{f, g} = w^ij \partial_i f \partial_j g
where [w^ij ] is the inverse of [w_ij ].
SHOW that
1) The Poisson bracket is well-defined, i.e., on the intersection of two
coordinate patches, the two definitions, one written in each local co-
ordinate system, actually always agree.
2) {f, g} = -{g, f} and
{f, gh} = {f, g}h + g{f, h}
for any three smooth functions f, g, h.
3) {f, {g, h}} + {g, {h, f}} + {h, {f, g}} = 0
for any three smooth functions f, g, h.

Thank you very much for taking time to consider these problems.

Sarason
 
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Erm, the answer is to "just do it".

calculate {f,g} on the overlap of two elements in the atlas and use the transformation rules for f and g (it's a smooth function) to show they are equal.

2 and 3, it now suffices to work locally, so do so.

it's not pleasant but that's the way it works I'm afraid.
 
Thanks for your reply. Would you please cite some
references so that I may consult the transformation rules
or the information related to my questions.

Sarason
 
Eh? any book on differential geometry or differential manifolds, or even differentiable manifolds will tell you what it means for a function to be smooth on the manifold. If you've not seen this then trying to do poisson brackets is a little adventurous.
 

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