# simple conditions equation

I tested some solutions, but without getting the simple results. aesthetic I would like to use the arrows. rather than parentheses. the formula is followed by a text with explanations of the conditions. would you have some simple suggestions about it? thanks

\documentclass[a4paper]{article}

\usepackage[T1]{fontenc}
\usepackage[italian]{babel}
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{mwe}
\usepackage{lmodern}
\makeatletter
\DeclareMathSizes{\@xpt}{\@xpt}{5}{4}
\DeclareMathSizes{\@xipt}{\@xipt}{6}{5}
\DeclareMathSizes{\@xiipt}{\@xiipt}{6}{5}
\DeclareMathSizes{\@xivpt}{\@xivpt}{\@xpt}{6}
\makeatother

\begin{document}
$\alpha = m\frac{l'\,z}{l_{0}}\; \begin{cases} >0\\=0\\<0 \end{cases}$

$\alpha = m\frac{l'\,z}{l_{0}} \begin{array}{c} \nearrow >0\\ \rightarrow = 0\\ \searrow < 0\\ \end{array}$
\end{document}


------------UPDATE------------------

this is what I wanted to get :

\begin{center}
\begin{subequations}
\begin{minipage}{.32\textwidth}
\centering
\begin{aligned} P_{G} = \frac{1}{\rho_{z}}gz_{,i}(\overline{\rho'u_{i}'})\label{eq097.4a} \end{aligned}
\end{minipage}\hfil
\begin{minipage}{.30 \textwidth}
%\centering
\begin{aligned} P_{G} = \frac{1}{\rho_{z}}g(\overline{\rho' w'})\label{eq097.4b} \end{aligned}
\end{minipage}\hfill
\begin{minipage}{.35 \textwidth}
\begin{aligned} P_{G} = g\frac{\overline{\theta' w'}}{\theta_{0}}\label{eq097.4c}\; \begin{array}{c@{\;}l} &>0\-.75ex] \nearrow\\ \rightarrow &= 0\\ \searrow\\[-.5ex] &< 0 \end{array} \end{aligned} \end{minipage}%\hfill \end{subequations} \end{center}  • Could you post an example of the kind of text you'd like to add? – Bernard Apr 27 at 21:37 • so far i not see anywhere your second example for writing "condition equation". cases is normal for such cases. it is far more readable than your "invention" ... – Zarko Apr 27 at 21:40 • @Bernard the equation I would like to explain is more complex. It is the conditions with respect to the production of buoyancy forces compared to the Richardson number. I am not very familiar with the tikz library and often I have difficulty with trivial things (which are often the most important ones) – Antonio Apr 27 at 22:38 • @Bernard in this case it is only an aesthetic problem. I prefer the arrows, to the braces – Antonio Apr 27 at 22:39 • Would there be an explanation per case, or a global explanation? – Bernard Apr 27 at 22:42 ## 3 Answers Using two columns in the array environment: \documentclass{article} \begin{document}  \alpha = m\frac{l'\,z}{l_{0}} \begin{array}{c@{\;}l} &>0\\[-.75ex] \nearrow\\ \rightarrow &= 0\\ \searrow\\[-.5ex] &< 0 \end{array}  \end{document}  • this could be an excellent and simple solution – Antonio Apr 28 at 10:39 • My compliment also to you. (+1) – Sebastiano Apr 28 at 15:28 My suggestion for example, for the 2nd formula, without left bracket, is with the package tikz-cd. \documentclass{article} \usepackage{tikz-cd} \usepackage{amsmath} \begin{document} \begin{tikzcd}[row sep=.4cm, column sep=.5cm] & >0 \\ {\alpha = m\dfrac{l'\,z}{l_{0}}} \arrow[ru] \arrow[r] \arrow[rd] & =0 \\ & <0 \end{tikzcd} \end{document}  • this is a good solution, but I need to enter the equation number – Antonio Apr 28 at 10:35 • @Antonio Thank you for that. Sorry for English (I'm like you Italian but in English I'm a landslide :-() but you could adapt my code very well, for example, reducing with the option row sep or column sep the length of the vectors to have a result very similar to what you want to get. Try changing the centimetres in the two options. – Sebastiano Apr 28 at 15:37 Done here with two separate stacks, so that the arrow vertical gap can be different than the baselineskip of the conditions stack. \documentclass[a4paper]{article} \usepackage[T1]{fontenc} \usepackage[italian]{babel} \usepackage{amsmath} \usepackage{tikz} \usepackage{mwe} \usepackage{lmodern} \makeatletter \DeclareMathSizes{\@xpt}{\@xpt}{5}{4} \DeclareMathSizes{\@xipt}{\@xipt}{6}{5} \DeclareMathSizes{\@xiipt}{\@xiipt}{6}{5} \DeclareMathSizes{\@xivpt}{\@xivpt}{\@xpt}{6} \makeatother \usepackage[usestackEOL]{stackengine} \stackMath \newcommand\arrowstack{\,\ensurestackMath{\stackengine{\Sstackgap}{% \stackengine{\Sstackgap}{\rightarrow}{\nearrow}{O}{c}{F}{F}{S}% }{\searrow}{U}{c}{F}{F}{S}% }} \begin{document} \[ \setstackgap{L}{16pt}% GOVERNS THE CONDITIONS STACK BASELINESKIP \setstackgap{S}{2pt}% GOVERNS THE ARROW STACK GAP \alpha = m\frac{l'\,z}{l_{0}} \arrowstack \Centerstack[l]{{}>0\\{}=0\\{}<0}
\end{document}


• yours is a particular solution. I always have problems with \stackMath. I got errors with solutions that use this line several times. I think it's due to my not very professional preamble – Antonio Apr 28 at 18:20
• @Antonio \stackMath is a global declaration switch. By default, or after a \stackText, stacking is done in text mode. With with the \stackMath switch set, it is done in math mode. If all your stacking is done in math, you need only set it once in the preamble. If you stack often enough so that some stacks are in text and others are in math, I recommend letting the default stay in text mode and wrapping math stacks in \ensurestackMath{...}. – Steven B. Segletes Apr 28 at 19:35