# Underset arrows of various lengths in aligned equation

I'm trying since some time now to get the following (see picture) done in LaTeX.

But I don't even have code that works so far, as all I've found by searching the internet wasn't helpful (I'm not even sure what to search for tbh).

I'd like the t's to be aligned with the v's and then draw the arrows like shown below. That t_1 \in T on the left side, isn't that important, as I'll just write that down below :)

I'm really stuck so any help would be appreciated!

EDIT: I've got the alignment although that isn't good practice I guess:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align*}
&cv_1 &&cv_2 &\ldots &&&cv_i &\ldots &&&&cv_j  &&\ldots &&&&&cv_k\\
&t_1  &&t_2 &\ldots &&&t_i &\ldots &&&&t_j  &&\ldots &&&&&t_k
\end{align*}
\end{document}

• Why not try tikz? Jan 28 at 17:41
• Tryed but couldn't do it...my tikz skills are too low i guess :P Jan 28 at 17:58

Here is a solution with a simple array environment andpstricks; the letters to be linked are defined as nodes in this array, and connected with \ncangle with the relevant parameters:

\documentclass{article}
\usepackage{amsmath}
\usepackage{array, makecell}
\usepackage{pst-node}

\begin{document}

$\begin{array}{*{9}{r}} cv_1 &cv_2 &\ldots &cv_i &\ldots &cv_j &\ldots &cv_k\\ t_1 & \rnode{T2}{t_2} &\ldots & \rnode{Ti}{t_i }&\ldots &\rnode{Tj}{t_j} &\ldots &t_k \\[0.5ex] & & & & & & & & \makecell{\rnode{Aj}{\varphi}\\\rnode{Ai}{\varphi}\\\rnode{A2}{\varphi}} \end{array} \psset{linewidth=0.6pt, linejoin=1, arrows=->, arrowinset=0.12, angleA=-90, angleB=180, nodesep=3pt} \foreach \s in {2,i, j}{\ncangle{T\s}{A\s}}$%

\end{document}


• Seems like a nice solution! Thank you a lot! :) I get "undefined controll sequence" tho when using it, because "\ncangle" isn't known? Jan 28 at 14:38
• It is documented. Maybe you compiled with pdflatex? Jan 28 at 14:44
• Ahm yes....ok so thats not working...gonna change it..thanks :) Edit: That solved it! Thanks so much! Jan 28 at 14:45
• Use xelatex, it will be simpler. Jan 28 at 14:47

I'm adapting my answer to "How to add arrow in equations and matrix?"; see there for some explanations on how to use Tikz to draw arrows between text elements.

• First, typeset the text without arrows.
• Wrap all elements, that will be the origin or target of an arrow, into a \tikznode command. This assigns a name to the text element and stores its size and position.
• Add a tikzpicture environment with the options remember picture,overlay below. It contains the graphical elements, in this case the arrows. Here you will use the names assigned in the previous step.
• Run LaTeX at least two times to propagate the information about the nodes and arrows everywhere.

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{arrows}% only needed for the arrow tip stealth'
\newcommand\tikznode[3][]{%
\tikz[remember picture,baseline=(#2.base)]
\node[minimum size=0pt,inner sep=0pt,#1](#2){#3};%
}
\begin{document}

$\begin{array}{*{9}{r}} cv_1 &cv_2 &\ldots &cv_i &\ldots &cv_j &\ldots &cv_k\\ t_1 & \tikznode{T2}{t_2} &\ldots & \tikznode{Ti}{t_i}&\ldots &\tikznode{Tj}{t_j} &\ldots &t_k \\[0.5ex] & & & & & & & & \tikznode{Aj}{\varphi} \\ & & & & & & & & \tikznode{Ai}{\varphi} \\ & & & & & & & & \tikznode{A2}{\varphi} \end{array}$%
\begin{tikzpicture}[remember picture,overlay,> = stealth',shorten <=3pt,shorten >=3pt]
\draw[->] (T2) |- (A2);
\draw[->] (Ti) |- (Ai);
\draw[->] (Tj) |- (Aj);
\end{tikzpicture}
\end{document}