#+title:Lagrange Mechanics
#+author: Thomas Albers Raviola
#+date: 2022-10-01
#+setupfile: ../../math_options.org

* Disclaimer
This site as of now just a technology demonstration and its claims
should not be taken as true (even though I myself am pretty confident
they are)

* Eliminating the constraints
\begin{align*}
m_i \ddot{x}_i &= F_i + \sum_{n=1}^R \lambda_n \pderiv{g_n}{x_i}\\
m_i \ddot{x}_i \pderiv{x_i}{q_k} &= F_i \pderiv{x_i}{q_k} + \sum_{n=1}^R \lambda_n \pderiv{g_n}{x_i} \pderiv{x_i}{q_k}\\
\sum_{i=1}^{3N} m_i \ddot{x}_i \pderiv{x_i}{q_k} &= \sum_{i=1}^{3N}F_i \pderiv{x_i}{q_k} + \sum_{n=1}^R \lambda_n \sum_{i=1}^{3N} \pderiv{g_n}{x_i} \pderiv{x_i}{q_k}\\
\sum_{i=1}^{3N} m_i \ddot{x}_i \pderiv{x_i}{q_k} &= \sum_{i=1}^{3N}F_i \pderiv{x_i}{q_k} + \sum_{n=1}^R \lambda_n \deriv{g_n}{q_k}\\
\sum_{i=1}^{3N} m_i \ddot{x}_i \pderiv{x_i}{q_k} &= \sum_{i=1}^{3N}F_i \pderiv{x_i}{q_k}\\
\deriv{}{t}\pderiv{(T - U)}{\dot{q}_k} - \pderiv{T}{q_k} &= \sum_{i=1}^{3N}F_i \pderiv{x_i}{q_k}\\
\deriv{}{t}\pderiv{(T - U)}{\dot{q}_k} - \pderiv{T}{q_k} &= - \sum_{i=1}^{3N}\pderiv{U}{x_i} \pderiv{x_i}{q_k}\\
\deriv{}{t}\pderiv{(T - U)}{\dot{q}_k} - \left(\pderiv{T}{q_k} - \pderiv{U}{q_k}\right) &= 0\\
\deriv{}{t}\pderiv{(T - U)}{\dot{q}_k} - \pderiv{T - U}{q_k} &= 0\\
\deriv{}{t}\pderiv{\mathcal{L}}{\dot{q}_k} - \pderiv{\mathcal{L}}{q_k} &= 0
\end{align*}