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Fixes, including disappearing arguments
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Signed-off-by: Marcello Seri <[email protected]>
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mseri committed Sep 21, 2024
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20 changes: 10 additions & 10 deletions hm.tex
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Expand Up @@ -77,6 +77,7 @@
\let\forlistloop\etoolboxforlistloop

\begin{warpprint}
\usepackage{picins}
%\usepackage[numbers, sort]{natbib}
%\setlength{\bibsep}{3pt}
%\renewcommand{\bibfont}{\small}
Expand Down Expand Up @@ -860,12 +861,12 @@ \chapter*{Preface}
\begin{remark}
Often in physics, the kinetic energy is instead defined as \emph{the work required to bring the mass from rest to some speed~$\dot{\vb{x}}$}.
One can then perform the computation above backwards
\begin{equation}
\begin{align}
\int_{x_0}^{x^1} \left\langle\vb*{F}(\vb*{x}), \dd{\vb*{x}}\right\rangle
= \int_{t_0}^{t_1} \left\langle\dot{\vb*{x}}(t), \vb*{F}(\vb*{x}(t))\right\rangle\; \dd t
= \int_{t_0}^{t_1} m \langle\dot{\vb*{x}}(t), \ddot{\vb*{x}}(t)\rangle\; \dd t
&= \int_{t_0}^{t_1} \left\langle\dot{\vb*{x}}(t), \vb*{F}(\vb*{x}(t))\right\rangle\; \dd t \\
&= \int_{t_0}^{t_1} m \langle\dot{\vb*{x}}(t), \ddot{\vb*{x}}(t)\rangle\; \dd t
= \int_{t_0}^{t_1} \dv{t} \frac{m}{2} \langle\dot{\vb*{x}}(t), \dot{\vb*{x}}(t)\rangle \; \dd t,
\end{equation},
\end{align},
leading to the definition of kinetic energy as $T = \frac{m}{2} \|\dot{\vb{x}}\|^2$.
\end{remark}

Expand Down Expand Up @@ -1239,9 +1240,8 @@ \chapter*{Preface}
\begin{example}[Double pendulum]\label{ex:2pendulum}
A double pendulum consists of two point particles of masses $m_1$ and $m_2$, connected by massless rods of lengths $l_1$ and $l_2$. The first pendulum is attached to the ceiling by a fixed pivot while the second one is attached to the point particle of the first pendulum.
\warpprintonly{
\InsertBoxR{0}{
\includegraphics[width=0.3\textwidth]{images/HM-1-12.pdf}
}%
\parpic[r]{\includegraphics[width=0.3\textwidth]{images/HM-1-12.pdf}}
%
}
\warpHTMLonly{
\begin{figure}[htbp]
Expand Down Expand Up @@ -1320,7 +1320,7 @@ \chapter*{Preface}

\begin{figure}[ht]
\centering
\includegraphics[width=.75\linewidth,trim={0 50pt 0 50pt},clip]{images/lissajous.pdf}
\includegraphics[width=.75\linewidth]{images/lissajous.pdf}
\caption{Some casually selected Lissajous figures. The top right example (in orange) and the one in the center at the bottom (in purple) are degenerate closed curves squeezed to a line.}
\label{img:lissajous}
\end{figure}
Expand Down Expand Up @@ -1448,11 +1448,11 @@ \chapter*{Preface}
Mapping $\frac{\partial}{\partial q^i}$ to the $i$-th Euclidean basis versor $e_i$ of $\mathbb{R}^n$ allows you to consider tangent vectors in coordinates as genuine euclidean vectors applied at a specific point $q$.

The most immediate way to compute the components $\dot q^i$ is by using the definition of tangent vectors as class of equivalence of tangents to curves \cite[Chapter 2.5]{lectures:aom:seri}.
Let $\gamma:\mathbb{R} \to M$ be a curve such that $\gamma(0) = q$ and $\dv{\gamma}{t}|_{t=0} = v$, then $\dot q^i = \dv{}{t}(q^i\circ\gamma)|_{t=0}$ is given by the $i$th component of $\dv{}{t}(\phi\circ\gamma)|_{t=0}$.
Let $\gamma:\mathbb{R} \to M$ be a curve such that $\gamma(0) = q$ and $\dv{\gamma}{t}|_{t=0} = v$, then $\dot q^i = \dv{}{t}\/(q^i\circ\gamma)|_{t=0}$ is given by the $i$th component of $\dv{}{t}\/(\phi\circ\gamma)|_{t=0}$.

The notation used for the basis versors of the tangent space in coordinates is not casual: in differential geometry tangent vectors are also \emph{derivations}. If $f\in C^\infty(M)$, the space of smooth functions from $M$ to $\mathbb{R}$, one can compute that for any tangent vector $v\in T_qM$,
\begin{equation}
v(f)=\dv{}{t}(f\circ\gamma)\big|_{t=0}, \qquad \gamma(0) = q, \; \dot \gamma(0) = v.
v(f)=\dv{}{t}\/(f\circ\gamma) \big|_{t=0}, \qquad \gamma(0) = q, \; \dot \gamma(0) = v.
\end{equation}
In local coordinates this corresponds to computing the directional derivative of $f$ in the direction of $v$ at the point $q$: i.e. $v(f)$ can be identified with $\langle Df(q),v\rangle$.

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