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Vector section re-editing WIP
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pelegs committed Mar 6, 2023
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39 changes: 27 additions & 12 deletions chapters/linear_algebra_intuitive/vectors.tex
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Expand Up @@ -310,8 +310,9 @@ \subsection{Column representation}

\subsection{Cartesian coordiantes and the standard basis vectors}

The space $\Rs[2]$ can be placed inside a Cartesian coordinate system, such that the origin of all vectors is at the point $\bm{O}=(0,0)$ (see \autoref{fig:2d_vec_cartesian}). It is then very common to use the following two vectors as basis vectors: $\hat{x}$, a vector of norm $1$ pointing in the direction of the $x$-axis, and $\hat{y}$, a vector of norm $1$ pointing in the direction of the $y$-axis.
The space $\Rs[2]$ can be placed inside a Cartesian coordinate system, such that the origin of all vectors is at the point $\bm{O}=(0,0)$. It is then very common to use the following two vectors as basis vectors: $\xr{\hat{x}}$, a vector of norm $1$ pointing in the direction of the $x$-axis, and $\xb{\hat{y}}$, a vector of norm $1$ pointing in the direction of the $y$-axis:

\colorlet{xbcol}{black!30}
\begin{center}
\begin{tikzpicture}[]
\begin{axis}[
Expand All @@ -321,33 +322,47 @@ \subsection{Cartesian coordiantes and the standard basis vectors}
ymin=-2, ymax=2,
xtick={-2,-1,1,2},
ytick={-2,-1,1,2},
axis line style={xbcol},
tick style={xbcol},
ticklabel style={xbcol},
xlabel style={xbcol},
ylabel style={xbcol},
major grid style={black!2},
]
\draw[vector, xred] (0,0) -- (1,0) node[midway, below] {$\hat{x}$};
\draw[vector, xblue] (0,0) -- (0,1) node[midway, left] {$\hat{y}$};
\fill (0,0) circle (0.05);
\end{axis}
\end{tikzpicture}
\end{center}

Using these basis vectors, any vector $\vec{v}$ has components that are equal to the coordinates of the point at it head (see \autoref{fig:vectors_std_basis_coords}).

\begin{figure}
\centering
\begin{tikzpicture}[]
\begin{axis}[
vector plane,
width=10cm, height=10cm,
xmin=-5, xmax=5,
ymin=-5, ymax=5,
xmin=-3, xmax=3,
ymin=-3, ymax=3,
xticklabels={},
yticklabels={},
axis line style={black!30},
tick style={black!30},
grid=both,
major grid style={black!10},
minor grid style={black!5},
minor tick num=4,
]
\draw[vector, xred] (0,0) -- (2,3);
\draw[vector, xblue] (0,0) -- (-1,2);
\draw[vector, xgreen] (0,0) -- (-3,0);
\draw[vector, xpurple] (0,0) -- (-1,-3);
\draw[vector, xorange] (0,0) -- (0,-4);
\draw[vector, black] (0,0) -- (1,-1);
\fill (0,0) circle (0.1);
\draw[vector, xred] (0,0) -- (1,0) node[midway, below] (xh) {$\hat{x}$} node[anchor=north west] {$(1,0)$};
\draw[vector, xblue] (0,0) -- (0,1) node[midway, left] (yh) {$\hat{y}$} node[anchor=south east] {$(0,1)$};
\draw[vector, xpurple] (0,0) -- (2,1) node[midway, above] {$\vec{v}$} node[anchor=west] {$(2,1)$};
\draw[vector, xdarkgreen] (0,0) -- (-2.6,1.2) node[midway, above] {$\vec{u}$} node[anchor=south, xshift=5] {$(-2.6,1.2)$};
\draw[vector, xorange] (0,0) -- (-2,-2) node[midway, above] {$\vec{w}$} node[anchor=north east] {$(-2,-2)$};
\fill (0,0) circle (0.05);
\end{axis}
\end{tikzpicture}
\caption{Some $2$-dimensional vectors placed on a $2$-dimensional Cartesian coordinate system.}
\label{fig:2d_vec_cartesian}
\caption{The standard basis vectors $\xr{\hat{x}}=\colvec{\xr{1};\xb{0}}$ and $\xb{\hat{y}}=\colvec{\xr{0};\xb{1}}$ on a $2$-dimensional Cartesian coordinate system, together with the vectors $\xp{\vec{v}}=\colvec{\xr{2};\xb{1}}$, $\xdg{\vec{u}}=\colvec{\xr{-2.6};\xb{1.2}}$ and $\xo{\vec{w}}=\colvec{\xr{-2};\xb{-2}}$.}
\label{fig:vectors_std_basis_coords}
\end{figure}

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