# A possible improvement of witharrows package

I was looking at this question Please help me solve. i am trying where there is the image below.

In my comment I have suggested using the witharrows package. I don't know this package very well, but using this code fragment (pag. 30 of the documentation) I have an error:

! Undefined control sequence.
l.9 tikz-code = {\draw
(#1) -- ++(4.5cm,0) |- (#2) ;
?


The MWE is:

\documentclass{article}
\usepackage{amsmath,amssymb}
\usepackage{tikz,witharrows}
\begin{document}
\begin{DispWithArrows*}
[displaystyle,
ygap = 2mm,
ystart = 0mm,
tikz-code = {\draw (#1) -- ++(4.5cm,0) |- (#2) ;
\path (#1) -- (#2)
node[text width = 4.2cm, right, midway] {#3} ;}]
S_n
& = \frac1n \sum_{k=0}^{n-1}\cos\bigl(\tfrac{\pi}2\cdot\tfrac kn\bigr)
\end{DispWithArrows*}
\end{document}


The output should be the first line:

Is is possible to put $\cos x =\Re(e^{ix})$ externally and not internally by coloring the entire square arrow with a color of your choice?

I am not good at writing equations -- but I think this is what you want

\documentclass{article}
\usepackage{amsmath,amssymb}
\usepackage{tikz,witharrows}
\begin{document}
\begin{DispWithArrows*}%
[displaystyle,
ygap = 2mm,
ystart = 0mm,
tikz-code = {\draw [red,thick](#1) -- ++(4.5cm,0) |- (#2) ;%<---------new red, thick option
\path (#1) -- (#2)
node[text width = 4.2cm, right, midway, xshift=5cm] {#3} ;}]%<-------xshift option
S_n
& = \frac1n \sum_{k=0}^{n-1}\cos\bigl(\tfrac{\pi}2\cdot\tfrac kn\bigr)  \Arrow {we expand} \\
& = \frac1n \sum_{k=0}^{n-1}\cos\bigl(\tfrac{\pi}2\cdot\tfrac kn\bigr)
\end{DispWithArrows*}
\end{document}


OR

\documentclass{article}
\usepackage{amsmath,amssymb}
\usepackage{tikz,witharrows}
\begin{document}
\begin{DispWithArrows*}%
[displaystyle,
ygap = 2mm,
ystart = 0mm,
tikz-code = {\draw [red,thick,rounded corners](#1) -- ([xshift=2cm]#1)
-- node[rectangle, draw, auto = false, fill = gray!50, inner sep = 2pt] {\tiny #3}
([xshift=2cm]#2)
-- (#2);}]
S_n
& = \frac1n \sum_{k=0}^{n-1}\cos\bigl(\tfrac{\pi}2\cdot\tfrac kn\bigr)  \Arrow {we expand} \\
& = \frac1n \sum_{k=0}^{n-1}\cos\bigl(\tfrac{\pi}2\cdot\tfrac kn\bigr)
\end{DispWithArrows*}
\end{document}


• It's a good option, as are your other great answers with TikZ. My sincere congratulations to you and a cordial greeting to you and your family. :-) My best regards. Jul 31 at 11:12
• @Sebastiano, if answer met your requirement, you may accept it ;-) (by clicking on the check mark at top left side of answer). Thank you. Jul 31 at 14:33
• Don't worry. :-) I know the procedure :-). Truly I am waiting also the complete answer of @F. Pantigny for the correctness (see the comment below his answer). Best regards. Aug 2 at 12:17

You should write \begin{WithArrows*}%. Otherwise, the options at the following line are not recognized as options of the environment {WithArrows*}: there must be no space between \begin{WithArrows*} and the character [ (and the newline counts as space).

• I have tried your suggestion (+1) but I have an error: ! LaTeX Error: Environment WithArrows* undefined. See the LaTeX manual or LaTeX Companion for explanation. Type H <return> for immediate help.... l.5 \begin{WithArrows*} % ?  Jul 30 at 21:08
• In your opinion is there a complete answer to my question? Jul 30 at 21:09
• @Sebastiano: For the LaTeX error, I think that you have not the latest version of witharrows. For the complete answer, I will see. Jul 30 at 21:15
• Yesterday I made the MikTeX updating...and I will wait....Grazieeeeeeeeeeeeeeeeeeeeeeeee. Jul 30 at 21:17
• Waiting Pantigny..I have given the check mark. :-) Aug 3 at 20:53