Poisson Brackets of Harmonic Oscillator

Theorem
Let $P$ be a classical harmonic oscillator.

Let the real-valued function $\map x t$ be the position of $P$, where $t$ is time.

Then $P$ has the following Poisson brackets:


 * $\sqbrk {x, p} = 1$


 * $\sqbrk {x, H} = \dfrac p m$


 * $\sqbrk {p, H} = - k x$

Proof
The standard Lagrangian of $P$ is:


 * $L = \dfrac 1 2 \paren {m {\dot x}^2 - k x^2}$.

The canonical momentum is:


 * $p = \dfrac {\partial L} {\partial \dot x} = m \dot x$

The Hamiltonian associated to $L$ in canonical coordinates reads:


 * $H = \dfrac {p^2} {2 m} + \dfrac k 2 x^2$

Then:


 * $\sqbrk {x, p} = \dfrac {\partial x} {\partial x} \dfrac {\partial p} {\partial p} - \dfrac {\partial p} {\partial x} \dfrac {\partial x} {\partial p} = 1$


 * $\sqbrk {x, H} = \dfrac {\partial x} {\partial x} \dfrac {\map \partial {\frac {p^2} {2 m} + \frac {k x^2} 2} } {\partial p} - \dfrac {\map \partial {\frac {p^2} {2 m} + \frac {k x^2} 2} } {\partial x} \dfrac {\partial x} {\partial p} = \dfrac p m$


 * $\sqbrk {p, H} = \dfrac {\partial p} {\partial x} \dfrac {\map \partial {\frac {p^2} {2 m} + \frac {k x^2} 2} } {\partial p} - \dfrac {\map \partial {\frac {p^2} {2 m} + \frac {k x^2} 2} } {\partial x} \dfrac {\partial p} {\partial p} = - k x$