|
1 | 1 | % !TeX spellcheck = en_GB
|
2 | 2 |
|
3 | 3 | \newglossaryentry{minimum}
|
4 |
| -{ |
5 |
| - name=minimum, |
6 |
| - description={Given a set of real numbers, the minimum\index{minimum} is the smallest of those numbers.}, |
7 |
| - first={minimum},text={minimum} |
| 4 | +{name=minimum, |
| 5 | + description={Given a set of real numbers, the minimum\index{minimum} is the smallest of those numbers.}, |
| 6 | + first={minimum},text={minimum} |
| 7 | +} |
| 8 | + |
| 9 | +\newglossaryentry{epigraph} |
| 10 | +{name={epigraph}, |
| 11 | + description={The epigraph\index{epigraph} of a real-valued function $f : \mathbb{R}^n \to \mathbb{R} \cup \{+\infty\}$ |
| 12 | + is the set of points lying on or above its graph: |
| 13 | + \[ |
| 14 | + \operatorname{epi}(f) = \left\{ (\mathbf{x}, t) \in \mathbb{R}^n \times \mathbb{R} \,\middle|\, f(\mathbf{x}) \leq t \right\}. |
| 15 | + \] |
| 16 | + A function is \gls{convex} if and only if its epigraph is a \gls{convex} set \cite{BoydConvexBook,BertCvxAnalOpt}. |
| 17 | + \begin{figure}[H] |
| 18 | + \centering |
| 19 | + \begin{tikzpicture}[scale=1.0] |
| 20 | + \begin{axis}[ |
| 21 | + axis lines = middle, |
| 22 | + xlabel = $x$, |
| 23 | + ylabel = {$$}, |
| 24 | + xmin=-2, xmax=2, |
| 25 | + ymin=0, ymax=4.5, |
| 26 | + samples=100, |
| 27 | + domain=-1.5:1.5, |
| 28 | + thick, |
| 29 | + width=8cm, |
| 30 | + height=6cm, |
| 31 | + grid=none, |
| 32 | + axis on top, |
| 33 | + ] |
| 34 | + % Function |
| 35 | + \addplot [blue, thick, domain=-1.5:1.5] {x^2} node [pos=0.85, anchor=south west, xshift=5pt] {$f(x)$}; |
| 36 | + % Epigraph shading |
| 37 | + \addplot [ |
| 38 | + name path=f, |
| 39 | + draw=none, |
| 40 | + ytick=\empty, |
| 41 | + domain=-1.5:1.5, |
| 42 | + ] {x^2}; |
| 43 | + \path[name path=top] (axis cs:-1.5,4) -- (axis cs:1.5,4); |
| 44 | + \addplot [ |
| 45 | + blue!20, |
| 46 | + opacity=0.6, |
| 47 | + draw=none, |
| 48 | + ] fill between [ |
| 49 | + of=f and top, |
| 50 | + soft clip={domain=-1.5:1.5}, |
| 51 | + ]; |
| 52 | + \node[font=\small] at (axis cs:-1.0,2.3) {$\operatorname{epi} f$}; |
| 53 | + % \node[align=center, fill=white, draw=black, rounded corners, font=\small] at (axis cs:0.5,3.5) {Epigraph\\$\{(x,t) \mid f(x) \le t\}$}; |
| 54 | + \end{axis} |
| 55 | + \end{tikzpicture} |
| 56 | + \caption{Epigraph of the function $f(x) = x^2$ (shaded area).} |
| 57 | + \end{figure} |
| 58 | + }, |
| 59 | + first={epigraph}, |
| 60 | + text={epigraph}, |
| 61 | + plural={epigraphs} |
8 | 62 | }
|
9 | 63 |
|
10 | 64 |
|
|
0 commit comments