The PreTeXt Guide

Subsubsection 4.14.3.1 Asymptote

<image xml:id="gaussian-histogram">
    <description>A histogram of Gaussian data.</description>
    <asymptote>
    import graph;
    import stats;

    size(400,200,IgnoreAspect);

    int n=10000;
    real[] a=new real[n];
    for(int i=0; i < n; ++i) a[i]=Gaussrand();

    draw(graph(Gaussian,min(a),max(a)),blue);

    // Optionally calculate "optimal" number
    // of bins a la Shimazaki and Shinomoto.
    int N=bins(a);

    histogram(a,min(a),max(a),N,normalize=true,low=0,lightred,black,bars=false);

    xaxis("$x$",BottomTop,LeftTicks);
    yaxis("$dP/dx$",LeftRight,RightTicks(trailingzero));
    </asymptote>
</image>

Subsubsection 4.14.3.2 Images in LaTeX Syntax

<docinfo>
    <latex-image-preamble>
    \usepackage{tikz}
    </latex-image-preamble>
</docinfo>

<figure>
    <caption>RNA Codons Table, by Florian Hollandt</caption>
    <image xml:id="rna-codons-table" width="100%">
        <description>A table of the RNA codons.</description>
        <latex-image>
        \begin{tikzpicture}
        \footnotesize
        \tikzstyle{every node}=[inner sep=1.7pt,anchor=center]
        % to_x and from_x styles denote bonds terminating
        % or starting in labeled nodes. x denotes the
        % number of letters in the node label.
        \tikzstyle{to_1}=[shorten >=5pt]
        \tikzstyle{to_1i}=[shorten >=6pt]
        \tikzstyle{to_2}=[shorten >=7pt]
        \tikzstyle{to_3}=[shorten >=8pt]
        ...
        \begin{scope}[scale=0.5]    % Asparagine
        \draw[ultra thick,shorten >=2pt,shorten &lt;=2pt] (90-2*5.625:8.2)
                        arc(90-2*5.625:90-4*5.625:8.2);
        \path (90-3.5*3.625-3:13.3) node (zero) {};
        \draw[to_2]  (zero.center)  -- ++(30:1) node (CO) {}
                        -- +(330:1) node [anchor=base] {O$^{\mbox{-}}$};
        \draw[to_1]  (CO.center)    -- +(90:1) node (Od) {O};
        \draw[to_1i] (CO.30)        -- +(90:1);
        \draw[to_3]  (zero.center)  -- ++(150:1) node {NH$_{\mbox{3}}^{\mbox{+}}$};
        \draw[to_2]  (zero.center)  -- ++(270:1) node(Cb){}
                        -- ++(330:1) node (Cc) {}
                        -- +(30:1) node (Cd) {NH$_{\mbox{2}}$};
        \draw[to_1i] (Cc.center)    -- +(270:1) node (O) {};
        \draw[to_1]  (Cc.210)       -- (O.150);
        \path (O.center) node {O};
        \end{scope}
        ...
        \node at (90-55*5.625:4.5) {C};
        \node at (90-58*5.625:4.5) {S};
        \node at (90-61*5.625:4.5) {L};
        \node at (90-63*5.625:4.5) {F};
        \end{tikzpicture}
        </latex-image>
    </image>
</figure>

Subsubsection 4.14.3.3 Scaling TikZ Images

The PreTeXt source below describes a simple TikZ picture, nd is followed by the picture itself. The rectangle is 8 centimeters wide. The Guide is produced as a PDF with 10 point text and a text width of \(6.5\) inches. (This is too wide for comfortable reading, and contrary to our recommendations. See Best Practice 30.6.1.) Normally, a choice of 10 point text would result in a width of \(340\) point, or about \(4.7\) inches.

So we compute the fraction of the available width required, as a percentage:

\begin{equation*} \frac{8\text{ cm}}{6.5\text{ in}} = \frac{8\text{ cm}\left(\frac{1\text{ in}}{2.54\text{ cm}}\right)}{6.5\text{ in}} = 0.4846 = 48.46\% \end{equation*}

and we use that as the width of the image.

<image xml:id="scaling-tikz" width="48.46%">
    <latex-image>
    \begin{tikzpicture}
    % 1 cm is default unit of length
    % a rectangle: 8 cm wide, 6 cm tall
    \draw[draw=black, thick] (4,2) rectangle (-4,-2);

    \node at (-2,  1) {Foo};
    \node at ( 2,  1) {Bar};
    \node at (-2, -1) {Baz};
    \node at ( 2, -1) {Qux};
    \end{tikzpicture}
    </latex-image>
</image>

Some characters for comparison: Foo  Bar  Baz  Qux

In the PDF version, the text matches between the image and the surrounding text almost identically. We could slide the image right and left by adjusting the margins (the default is to be centered). But if we want the image bigger and smaller, we need to adjust the TikZ code and recompute the @width attribute.

Now for HTML we need to produce an SVG version that is a close match. The HTML version is a close match for LaTeX built with a computed text width (for any font size). We do not want to change the percentage of the width devoted to the TikZ picture, and we do not want to change the TikZ code itself. If we had not chosen a different text width (the \(6.5\) inches, versus a computed \(340\) point), then we could generate the SVG by supplying the same publication file, so as to use the same font size. However, our text width is 38% larger in the LaTeX version,

\begin{equation*} \frac{6.5\text{ in}}{340\text{ pt}} = \frac{6.5\text{ in}\left(\frac{72.27\text{ pt}}{1\text{ in}}\right)}{340\text{ pt}} = 1.3816 \end{equation*}

The font size needs to increase by a similar percentage,

\begin{equation*} 10\text{ pt}\times 1.3816 = 13.816\text{ pt}\approx 14\text{ pt} \end{equation*}

So we generate the SVG image with a different publication file, giving a font size of 14 point. The HTML font in the text may be very different from the LaTeX font used in the TikZ picture, but their sizes are nearly identical. Note that our use of LaTeX only supports 8 different font sizes, so it was fortuitous in this example that the 38% increase was so close to the supported 14 point font size. Note also, that since we used a different text width for the PDF, the resulting 40% increase in the font size for the SVG could play havoc with text that has been placed carefully not to overlap other components of the picture.

Subsubsection 4.14.3.4 Images in Sage Syntax

<figure>
    <caption>Negative multiple of a curve</caption>
    <image xml:id="negative-curve" width="65%">
        <description>Plot of x^4 - 1 and its negative.</description>
        <sageplot>
        f(x) = x^4 - 1
        g(x) = -x^4 + 1
        up = plot(f, (x, -1.5, 1.5), color='blue', thickness=2)
        down = plot(g, (x, -1.5, 1.5), color='red', thickness=2)
        up + down
        </sageplot>
    </image>
</figure>