User em12 - MathOverflow most recent 30 from http://mathoverflow.net 2013-05-21T17:11:56Z http://mathoverflow.net/feeds/user/16101 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/69178/momentum-maps-and-matrix-poisson-brackets Momentum maps and matrix poisson brackets. em12 2011-06-30T11:49:27Z 2011-07-16T21:22:12Z <p>I'm trying to understand how this solution works. The question was to deduce momentum maps for right and left actions of $SO(3)$ on $GL(3,R)$, and got them as $J_R = \frac{1}{2}(Q^TP-P^TQ)$ and $J_L=\frac{1}{2}(PQ^T-QP^T)$ respectively, for $Q\in GL(3)$, $P\in GL(3)^*$. However, then I need to find if they Poisson commute. The solution is:</p> <p><code>$\{ J_L,J_R \} = \frac{1}{4}\{(PQ^T-QP^T),(Q^TP-P^TQ)\} = \frac{1}{4}((P-P^T)(Q-Q^T)-(Q^T-Q)(P-P^T))$</code></p> <p>But I don't understand how this works (specifically, how to compute a poisson bracket with matrices). There is no explicit definition of the poisson bracket in the solution. Elsewhere in the text there was a Poisson bracket defined as</p> <p><code>$\{F,H\}=tr(\frac{\partial F}{\partial Q}\frac{\partial H}{\partial P}-\frac{\partial H}{\partial Q}\frac{\partial F}{\partial P})$</code></p> <p>but that is for scalar functions $F,H$. I guess you could apply that formula to every entry of the $P,Q$'s but there must be a shortcut. Sorry if i've not given enough context, please ask. Thanks for any help.</p>