- #1
shedrick94
- 30
- 0
I'm just in need of some clearing up of how to differentiate the lagrangian with respect to the covariant derivatives when solving the E-L equation:
Say we have a lagrangian density field
\begin{equation}
\mathcal{L}=\frac{1}{2}(\partial_{\mu}\hat{\phi})(\partial^{\mu}\hat{\phi})
\end{equation}
When solving for E-L why does:
\begin{equation}
\frac{\partial \mathcal{L}}{\partial (\partial_{\mu}\phi)}= \partial^{\mu}\hat{\phi}
\end{equation}
i.e Why do we lose the factor of 1/2
Say we have a lagrangian density field
\begin{equation}
\mathcal{L}=\frac{1}{2}(\partial_{\mu}\hat{\phi})(\partial^{\mu}\hat{\phi})
\end{equation}
When solving for E-L why does:
\begin{equation}
\frac{\partial \mathcal{L}}{\partial (\partial_{\mu}\phi)}= \partial^{\mu}\hat{\phi}
\end{equation}
i.e Why do we lose the factor of 1/2