- #1
kulimer
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I am trying to understand how Hamiltonian gradient works.
U(q): potential energy
K(p): kinetic energy
q: position vector
p: momentum vector
both p and q are functions of time
H(q,p): total energy
[itex]H(q,p)=U(q)+K(p)[/itex]
U(q): potential energy
K(p): kinetic energy
q: position vector
p: momentum vector
both p and q are functions of time
H(q,p): total energy
[itex]\frac{d{{q}_{i}}}{dt}=\frac{\partial H}{\partial {{p}_{i}}}[/itex]
[itex]\frac{d{{p}_{i}}}{dt}=-\frac{\partial H}{\partial {{q}_{i}}}[/itex]
Now, I am trying to solve this (the technical name is called leapfrog method)[itex]\frac{d{{p}_{i}}}{dt}=-\frac{\partial H}{\partial {{q}_{i}}}[/itex]
[itex]{p}_{i}(t+\varepsilon /2)={p}_{i}(t)-(\varepsilon /2)\frac{\partial U}{\partial {q}_{i}}(q(t))[/itex]
[itex]{q}_{i}(t+\varepsilon )={q}_{i}(t)+\varepsilon \frac{{p}_{i}(t+\varepsilon /2)}{m}[/itex]
[itex]{p}_{i}(t+\varepsilon )={p}_{i}(t+\varepsilon /2)-(\varepsilon /2)\frac{\partial U}{\partial {q}_{i}}(q(t+\varepsilon ))[/itex]
[itex]{q}_{i}(t+\varepsilon )={q}_{i}(t)+\varepsilon \frac{{p}_{i}(t+\varepsilon /2)}{m}[/itex]
[itex]{p}_{i}(t+\varepsilon )={p}_{i}(t+\varepsilon /2)-(\varepsilon /2)\frac{\partial U}{\partial {q}_{i}}(q(t+\varepsilon ))[/itex]
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