I prepared the following document

\documentclass[12 pt]{report}
            $De = Re\sqrt{\frac{D}{2R_C}}$
            \draw[->] (-1.35,0.4) ..controls (-1.2,1) and (-0.5,1.5) .. (-0.2,1.5) node[right] {Reynolds number};
            \draw[->] (-2.35,0.4) .. controls (-2.35,0.9) and (-2.75,1)   .. (-3.5,0.3) node[left] {Dean number};
            \draw[->] (-0.15,0.3) .. controls (0.3,0.7) and (0.25,-0.4) .. (0.6,-0.3) node[right] {Hydraulic diameter};
            \draw[->] (-0.25,-0.275) .. controls (-0.5,-1)  .. (-1.5,-1) node[left] {Path curvature radius};

Which gives, enter image description here

But due to the math mode 'De' and 'Re' becomes italic, I don't want that. But if I try \text{} for 'De' and 'Re', it is not working. Please help me to change 'De' and 'Re' into a normal text instead of italic.

Also, I am new to tikz. So, is there any other way to create the pictorial definition of each term in a equation as shown in the picture above?

  • 2
    You can try \mathrm: $\mathrm{De} = \mathrm{Re}\sqrt{\frac{D}{2R_C}}$. May 2, 2021 at 16:33
  • 2
    Not related but you could have used tikzmark to create nodes and draw your arrows.
    – SebGlav
    May 2, 2021 at 17:09
  • I surprised that works at all, text placed directly inside a tikzpicture is normally ignored. You should place the equation in a node, like the other text you have in there. May 2, 2021 at 17:25
  • @JuanCastaño Thanks, it works and it is simple and easy! May 3, 2021 at 3:05

1 Answer 1


A solution using tikzmark library and accepting \text{}.

tikzmark equation


    \tikzset{every node/.style={outer sep=2pt}}

    \tikzmarknode{De}{\text{De}} = \tikzmarknode{Re}{\text{Re}}\sqrt{\frac{{\tikzmarknode{D}{D}}}{\tikzmarknode{2RC}{2R_C}}}
    \begin{tikzpicture}[remember picture,overlay]
        \draw[->] (De.north) to[out=90,in=45,looseness=1.5] ($(De)+(-1,0)$) node[left] {Dean number};
        \draw[->] (Re.north) to[out=90,in=180] ($(Re)+(1.2,1.2)$) node[right] {Reynolds number};
        \draw[->] (D.east) to[out=45,in=190] ($(D)+(1.5,-1)$) node[right] {Hydraulic diameter};
        \draw[->] (2RC.south) to[out=-90,in=0] ($(2RC)+(-1.5,-1)$) node[left] {Path curvature radius};

Note that you may need two compilations to make it right, since the nodes have to be computed before arrows could be drawn.

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