# Writing a worded mathematical expression

How to write the below expression in latex using equation or align. Edit: Changed the wordings based on the suggestion from @Henri Menke

• What is this supposed to do apart from being hard to read? – Henri Menke Sep 10 '19 at 8:46
• Probably be easy to read. You don't know the context or the audience, so you have no justification for jumping to such narrow-minded condescending criticism. If you want to offer neutral, constructive criticism, you could say "Would form X be clearer to read for your scenario?" and be fully open to a potential answer "No". – Apollys supports Monica Sep 10 '19 at 22:11

Very simple with stackengine:

\documentclass{article}

\usepackage{amsmath}
\usepackage[usestackEOL]{stackengine}

\begin{document}

$\begin{pmatrix} \Centerstack{Rate of heat \\ conduction \\at x} \end{pmatrix} - \begin{pmatrix} \Centerstack{Rate of heat \\ conduction \\at x+Δx} \end{pmatrix} + \begin{pmatrix} \Centerstack{Rate of heat \\ generation \\ inside the \\ element} \end{pmatrix} = \begin{pmatrix} \Centerstack{Rate of change \\ of the energy \\ content of the \\ element} \end{pmatrix}$%

\end{document} Decide which one is better in your context.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

This is the formula using words:
\begin{equation*}
\begin{pmatrix}\begin{tabular}{@{}c@{}}
Rate of heat \\ conduction \\ at $x$
\end{tabular}\end{pmatrix}
-
\begin{pmatrix}\begin{tabular}{@{}c@{}}
Rate of heat \\ conduction \\ at $x+\Delta x$
\end{tabular}\end{pmatrix}
+
\begin{pmatrix}\begin{tabular}{@{}c@{}}
Rate of heat \\ generation \\ inside the \\ element
\end{tabular}\end{pmatrix}
=
\begin{pmatrix}\begin{tabular}{@{}c@{}}
Rate of change\\ of the energy \\ content of the \\ element
\end{tabular}\end{pmatrix}
\end{equation*}

Let's denote by $R_{\mathrm{hc}}(x)$ the rate of heat conduction at~$x$,
by $R_{\mathrm{hgi}}$ the rate of heat generation inside the element and
by $\mathit{RC}_{\mathrm{ec}}$ the rate of change of the element's energy
content. Then
\begin{equation*}
R_{\mathrm{hc}}(x)-R_{\mathrm{hc}}(x+\Delta x)+R_{\mathrm{hgi}}
=\mathit{RC}_{\mathrm{ec}}
\end{equation*}

\end{document} • This seems to be a more elegant solution. Thanks @egreg . – Gowrishankar Hallilingaiah Sep 11 '19 at 7:04
• @egreg What does the command {@{}c@{}} of the tabular environment do? – Mark Fantini Sep 18 '19 at 0:43
• @MarkFantini It defines “one column with center alignment and no padding on either side”. – egreg Sep 18 '19 at 8:14

A new macro like \newcommand{\term}{\left(\begin{tabular}{@{}c@{}}#1\end{tabular}\right)} can be very handy in this case:

\documentclass{article}

\newcommand{\term}{\left(\begin{tabular}{@{}c@{}}#1\end{tabular}\right)}

\begin{document}

This is the formula using words:
$\term{Rate of heat\\ conduction\\ at x} - \term{Rate of heat\\ conduction\\ at x+\Delta x} + \term{Rate of heat\\ generation\\ inside the\\ element} = \term{Rate of change\\ of the energy\\ content of the\\ element}$

\end{document} \documentclass{book}

\usepackage{amsmath}

\begin{document}

\begin{equation*}

\left(\begin{array}{c}
\text{Rate of heat}\\
\text{conduction}\\
\text{at } x
\end{array}\right)-
\left(\begin{array}{c}
\text{Rate of heat}\\
\text{conduction}\\
\text{at } x + \triangle x
\end{array}\right) +
\left(\begin{array}{c}
\text{Rate of heat}\\
\text{generation}\\
\text{inside the}\\
\text{element}
\end{array}\right) =
\left(\begin{array}{c}
\text{Rate of change}\\
\text{of the energy}\\
\text{content of the}\\
\text{element}
\end{array}\right)

\end{equation*}

\end{document} • Semantically, I think array should only enclose arrays of mathematical expressions; you've put lines of text in one and tabular is probably the better environment for that. Or maybe even a \parbox. – Matthew Leingang Sep 11 '19 at 0:01
• Surely we want \Delta here, not \triangle. – Richard Sullivan Sep 11 '19 at 13:49

A solution using TikZ, with its internal aligns, to do a verbal equation (hence as spoken aloud and with symbolics minimised) of what are, in effect, conceptual automata; and, since the inflow and outflow happen concurrently, removing the linearity implied by the algebraic algorithm and re-arranging to show that energy in/out simultaneity feeding into the outcome. Plus some colour coding, hot and cold.

A true visual representation would have a receptacle icon to hold the energy while it is in flux (like a cup), a pour-in icon (like a teapot, say), a pour-out icon (like air and a saucer), and a time dimension (animation?).

Not an equation in the narrow sense, though. So not really an answer.

MWE:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{automata,positioning}

\begin{document}
\begin{tikzpicture}[%
>=stealth,
node distance=2cm,
on grid,
auto
]
\node[state] (A)              [align=center,fill=blue!5,text width=2cm]{Rate of heat conduction at  $x$};
\node        (A1) [align=center,below right=of A,text width=2em]{\textit{minus}};
\node        (B) [align=center,right= of A1,fill=green!15,text width=2cm]{Rate of heat conduction at  $x + \Delta x$};
\node        (B1) [align=center,above right=of A,text width=2em]{\textit{plus}};
\node        (C) [align=center,right= of B1,fill=red!5,text width=2cm]{Rate of heat generation inside the element};
\node        (C2) [align=center, right=of A]{};
\node        (C3) [align=center, right=of C2]{};
\node        (C1) [align=center, right=of C3,text width=2cm]{\textit{equals}};
\node        (C4) [align=center, right=of C1]{};
\node        (D) [state,node distance=1cm,align=center,right= of C4,fill=blue!5,text width=2cm]{Rate of change of the energy content of the element};
\end{tikzpicture}
\end{document}