Comment #27 on issue 1816 by Vinzent.Steinberg: Adding partial derivatives
and taking derivatives with respect to functions
http://code.google.com/p/sympy/issues/detail?id=1816
Can you cite an example of somewhere where this is computed as so with
the Lagrangian?
The simplest possible Lagrangian I can think of (a freely moving mass
particle with no force acting on it):
L(x(t), x'(t), t) = m/2 * x'(t)
=>
d/dt \partial L(x(t), x'(t), t) / \partial x'(t) - \partial L(x(t), x'(t),
t) / \partial x(t) == 0
=> m x''(t) == 0
The second term in the sum of the Euler-Lagrange equation is clearly zero,
hence diff(x'(t), x(t)) == 0.
Maybe we are mixing partial and total derivatives?
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