[Tex/LaTex] How to draw good arrows explaining parts of equation

math-modetikz-pgf

I want to point out what the different parts of an equation is by arrows pointing into the equation. By using the \tikzmark command from Adding a large brace next to a body of text I have managed to come up with this:

\documentclass[12pt]{memoir}
\usepackage[cmintegrals,cmbraces]{newtxmath}
\usepackage{ebgaramond-maths}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{calc}

\newcommand{\tikzmark}[1]{\tikz[overlay,remember picture] \node (#1) {};}

\begin{document}
{\Large
\begin{equation*}
 V\tikzmark{V} = V\tikzmark{Vp}_p + V\tikzmark{Vt}_t\frac{fu\tikzmark{fu}}{fu_t\tikzmark{fut}}
\end{equation*}
\begin{tikzpicture}[overlay,remember picture]
    \node (Ve) [below of = V, node distance = 3.5 em]{\footnotesize \textsf{Distribution volume}};
    \draw[<-, in=180, out=-90] (V.south) to (Ve.west);

    \node (Vpe) [below of = Vp, node distance = 2.5 em] {\footnotesize \textsf{Volume water in plasma}};
    \draw[<-, in=180, out=-90] (Vp.south) to (Vpe.west);

    \node (Vte) [below of = Vt, node distance = 1.5 em] {\footnotesize \textsf{Volume water in tissue}};
    \draw[<-, in=180, out=-90] (Vt.south) to (Vte.west);

    \node (fue) [right of = fu, node distance = 6 em] {\footnotesize \textsf{Fraction unbound drug in plasma}};
    \draw[<-] (fu.east) to (fue.west);

    \node (fute) [right of = fut, node distance = 6 em] {\footnotesize \textsf{Fraction unbound drug in tissue}};
    \draw[<-] (fut.east) to (fute.west);

\end{tikzpicture}
}
\end{document}

However, the \tikzmark command doesn't really work for me cause I can't use it to point directly to one particular glyph. Furthermore I am having serious trouble making the arrows point to the beginning of the text and at the same time place the text so that it doesn't overlap. Seems like I would want the beginning of the text to be underneath and not the center. What is the tricks that I am missing here?

Best Answer

With the help of Highlighting equation with arrow and the anchor=west command, here is one way of doing it:

\documentclass[12pt]{memoir}
\usepackage[cmintegrals,cmbraces]{newtxmath}
\usepackage{ebgaramond-maths}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{calc}

\newcommand{\tikzmark}[1]{\tikz[baseline,remember picture] \coordinate (#1) {};}

\begin{document}
{\Large
\begin{equation*}
 \tikzmark{V}V = \tikzmark{Vp}V_p + \tikzmark{Vt}V_t\frac{\tikzmark{fu}fu}{\tikzmark{fut}fu_t}
\end{equation*}
\begin{tikzpicture}[overlay,remember picture]
    \node (Ve) [below of = V, node distance = 4 em, anchor=west]{\footnotesize \textsf{Distribution volume}};
    \draw[<-, in=180, out=-90] (V.south)++(.25em,-.5ex) to (Ve.west);

    \node (Vpe) [below of = Vp, node distance = 3 em, anchor=west] {\footnotesize \textsf{Volume water in plasma}};
    \draw[<-, in=180, out=-90] (Vp.south)++(.25em,-.5ex) to (Vpe.west);

    \node (Vte) [below of = Vt, node distance = 2 em, anchor=west] {\footnotesize \textsf{Volume water in tissue}};
    \draw[<-, in=180, out=-90] (Vt.south)++(.25em,-.5ex) to (Vte.west);

    \node (fue) [right of = fu, node distance = 6.5 em] {\footnotesize \textsf{Fraction unbound drug in plasma}};
    \draw[<-] (fu.east)++(1.2em,0.5ex) to (fue.west);

    \node (fute) [right of = fut, node distance = 6.5 em] {\footnotesize \textsf{Fraction unbound drug in tissue}};
    \draw[<-] (fut.east)++(1.2em,0.5ex) to (fute.west);

\end{tikzpicture}
}
\end{document}

Related Solutions

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

The source of the difficulty is that ellipses are constructed in a particular way in TikZ. They are paths that start from the x-axis and proceed counter-clockwise around their centre. The vast majority of the time, the exact parametrisation doesn't matter. You appear to have found the one situation where it does!

In the actual question, you only want to be able to mirror the ellipse, and so draw it starting from the negative x-axis (the title of the question suggests a more flexible approach). That's actually not too hard since we can exploit the symmetry of the ellipse. The key is to provide it with a negative x-radius, since then it will start from the negative x-axis (and proceed clockwise, but we could correct for that by negating the y-radius as well). To do this, we interrupt the call from the node shape to the drawing command and flip the sign of the x-radius. The simplest way to do this is to redefine the \pgfpathellipse macro to do the negation and then call the original macro. The following code does this.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations,shapes,decorations.markings}
\makeatletter
\let\origpgfpathellipse=\pgfpathellipse
\def\revpgfpathellipse#1#2#3{%
  #2%
  \pgf@xa=-\pgf@x
  \origpgfpathellipse{#1}{\pgfqpoint{\pgf@xa}{0pt}}{#3}}
\makeatother

\tikzset{
  reversed ellipse/.style={
    ellipse,
    reverse the ellipse%
  },
  reverse the ellipse/.code={
    \let\pgfpathellipse=\revpgfpathellipse
  }
}
\begin{document}
\begin{tikzpicture}
\node[ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,0) {hello world};

\node[reversed ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,-2) {hello world};
\end{tikzpicture}

\end{document}

Here's the result:

rotated ellipse

(the arrow got clipped, but you can see where it lies)

[Tex/LaTex] How to define the default vertical distance between nodes

I don't really get the question so I hope this is what you wanted. If you include a full document (such that we copy paste and see the problem on our systems) things are much more easier.

Here, you can change the default setting within a scope but your block style had a node distance which was resetting every time it is issued. I've made it 2mm such that we can see the difference easier.

\documentclass[tikz]{standalone}
\usetikzlibrary{arrows,shapes.geometric,positioning}

\begin{document}
\begin{tikzpicture}[decision/.style={diamond, draw, text width=4.5em, text badly centered, node distance=3.5cm, inner sep=0pt},
                    block/.style   ={rectangle, draw, text width=6em, text centered, rounded corners, minimum height=4em, minimum height=2em},
                    cloud/.style   ={draw, ellipse, minimum height=2em},
                    line/.style    ={draw,-latex'},
                    node distance = 1cm, 
                    auto]
    \node [block] (1st) {1st};
    \node [block, right= of 1st]  (2nd1) {2nd1};
\begin{scope}[node distance=2mm and 10mm]%Here we change it for everything inside this scope
    \node [block, above= of 2nd1] (2nd2) {2nd2};
    \node [block, below= of 2nd1] (2nd3) {2nd3};
    \node [block, right= of 2nd1] (3rd1) {3rd1};
    \node [block, above= of 3rd1] (3rd2) {3rd2};
    \node [block, above= of 3rd2] (3rd3) {3rd3};
\end{scope}
    \node [block, below= of 3rd1] (3rd4) {3rd4};
    \node [block, below= of 3rd4] (3rd5) {3rd5};

    \path [line] (1st) -- (2nd1);
    \path [line] (2nd1) -- (2nd2);
    \path [line] (2nd1) -- (2nd3);
    \path [line] (2nd2) -- (3rd3);
    \path [line] (2nd1) -- (3rd1);
    \path [line] (1st) -- (2nd1);
\end{tikzpicture}
\end{document}

enter image description here

Best Answer

Related Solutions

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

[Tex/LaTex] How to define the default vertical distance between nodes

Related Question