On a conditional command: more powerful than \ifnum

Question

According to the TEX in a Nutshell, Petr Olšák, page 16/29, we get:

\ifnum ⟨number 1⟩ ⟨relation⟩ ⟨number 2⟩ . The ⟨relation⟩ could be < or = or >. It returns true if the comparison of the two numbers is true.

I am looking for a more powerful conditional command to include (~=) (not equal to) relation.

Do we have such a conditional command?

The reason I asked is related to page 1005/1318 TikZ manual. Which I modified the code a little bit to generate an array of elliptical objects as below:

I rotated all ellipses 45 degree clockwise. What I want to do is not to rotate the highlighted ellipses in yellow so the rot=0 for them.

How to do it with a conditional command?

Below is my code:

 \documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
 \foreach \x in {1,...,4}
\foreach \y in {1,...,4}
{
\fill[red!50] (\x,\y) ellipse [x radius=3pt, y radius=6pt, rotate=-45];
\ifnum {\x<\y} & {\x>1}
\breakforeach
\fi
}
\draw [|-|] (.895,1) -- ++(0.211,0);
\end{tikzpicture}
\end{document}

It seems ifthen package is the answer. I used the code below using \ifthenelse, but got an error:

\documentclass{standalone}
\usepackage{tikz,ifthen}
\begin{document}
\ifthenelse{1>2 \AND 3=3}{yes}{no}
\begin{tikzpicture}
\foreach \x in {1,...,4}
\foreach \y in {1,...,4}
{
\newcommand{\first}{\(\x=1 \and \y=1\)}
\newcommand{\second}{\(\x=2 \and \y=1\) }
\ifthenelse{\(\first\) \or \(\second\)}
 {\fill[red!50] (\x,\y) ellipse [x radius=3pt , y radius= 6pt, rotate=0];}
{\fill[red!50] (\x,\y) ellipse [x radius=3pt , y radius= 6pt, rotate=-45];}
\ifnum \x<\y
\breakforeach
\fi
}
\draw [|-|] (.895,1) -- ++(0.211,0);
\end{tikzpicture}
\end{document}

Error: ! Extra \or. ...=1) } \ifthenelse {(\first ) \or (\second )} {\fill [red!... Do you know how to debug this code to make it work?

egreg · Accepted Answer · 2020-08-05T09:27:50.533

In order to reproduce the picture, the test should be 1 ≤ x < y.

You can parametrize the rotation angle and test for the two special cases.

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\foreach \x in {1,...,4} {
  \foreach \y in {1,...,4} {
    \def\rotation{-45}
    \ifnum\y=1
      \ifnum\x=1 \def\rotation{0} \fi
      \ifnum\x=2 \def\rotation{0} \fi
    \fi
    \fill[red!50] (\x,\y) ellipse [x radius=3pt, y radius=6pt, rotate=\rotation];
    \ifnum \x<\y \unless\ifnum \x<1 \breakforeach \fi\fi
  }
}
\draw [|-|] (.895,1) -- ++(0.211,0);
\end{tikzpicture}
\end{document}

You can also use \ifthenelse, of course.

\documentclass{standalone}
\usepackage{tikz}
\usepackage{xifthen}
\begin{document}
\begin{tikzpicture}
\foreach \x in {1,...,4} {
  \foreach \y in {1,...,4} {
    \ifthenelse{\y=1 \AND (\x=1 \OR \x=2)}{\def\rotation{0}}{\def\rotation{-45}}
    \fill[red!50] (\x,\y) ellipse [x radius=3pt, y radius=6pt, rotate=\rotation];
    \ifthenelse{ \x<\y \AND \NOT(\x<1) }{\breakforeach}{}
  }
}
\draw [|-|] (.895,1) -- ++(0.211,0);
\end{tikzpicture}
\end{document}

With a somewhat easier syntax, see https://tex.stackexchange.com/a/467527/4427

\documentclass[border=4]{standalone}
\usepackage{tikz}
\usepackage{xparse}
\ExplSyntaxOn
\NewExpandableDocumentCommand{\xifthenelse}{mmm}
 {
  \bool_if:nTF { #1 } { #2 } { #3 }
 }
\cs_new_eq:NN \numtest     \int_compare_p:n
\cs_new_eq:NN \oddtest     \int_if_odd_p:n
\cs_new_eq:NN \fptest      \fp_compare_p:n
\cs_new_eq:NN \dimtest     \dim_compare_p:n
\cs_new_eq:NN \deftest     \cs_if_exist_p:N
\cs_new_eq:NN \namedeftest \cs_if_exist_p:c
\cs_new_eq:NN \eqdeftest   \token_if_eq_meaning_p:NN
\cs_new_eq:NN \streqtest   \str_if_eq_p:ee
\cs_new_eq:NN \emptytest   \tl_if_blank_p:n
\prg_new_conditional:Nnn \xxifthen_legacy_conditional:n { p,T,F,TF }
 {
  \use:c { if#1 } \prg_return_true: \else: \prg_return_false: \fi:
 }
\cs_new_eq:NN \boolean \xxifthen_legacy_conditional_p:n
\ExplSyntaxOff
\begin{document}
\begin{tikzpicture}
\foreach \x in {1,...,4} {
  \foreach \y in {1,...,4} {
    \xifthenelse{\numtest{\y=1} && (\numtest{\x=1} || \numtest{\x=2})}
      {\def\rotation{0}}
      {\def\rotation{-45}}
    \fill[red!50] (\x,\y) ellipse [x radius=3pt, y radius=6pt, rotate=\rotation];
    \xifthenelse{ \numtest{1<=\x<\y} }{\breakforeach}{}
  }
}
\draw [|-|] (.895,1) -- ++(0.211,0);
\end{tikzpicture}
\end{document}

@Aria Is there any reason to? Anyway, I added it. – egreg Aug 05 '20 at 09:17 — egreg, Aug 05 '20 at 09:17
I thought if then else might be shorter. – Aria Aug 05 '20 at 17:04 — Aria, Aug 05 '20 at 17:04

score 6 · Answer 2 · answered Aug 05 '20 at 05:18

6

LaTeX's ifthen package has some facility for combining conditionals with \and and \or, \not and parentheses. But your case is easy to do with \ifnum:

\ifnum \x<\y \ifnum \x>1
  \breakforeach
\fi\fi

answered Aug 05 '20 at 05:18

Donald Arseneau

6,079

Can we get parentheses in \ifthenelse{(\x=1 \and \y=1) \or (\x=2 \and \y=1)}{}{}? – Aria Aug 05 '20 at 05:32
Do texdoc ifthen. The introduction is all the documentation you need to read. Parentheses need to be \( and \). – Donald Arseneau Aug 05 '20 at 06:50
Got error for: \newcommand{\first}{(\x=1 \and \y=1)} \newcommand{\second}{(\x=2 \and \y=1) } \ifthenelse{\first \or \second } {\fill[red!50] (\x,\y) ellipse [x radius=3pt , y radius= 6pt, rotate=0];} {\fill[red!50] (\x,\y) ellipse [x radius=3pt , y radius= 6pt, rotate=-45];} – Aria Aug 05 '20 at 06:59
I need to have a condition like (p and q) or (p and r), do you know how to define? – Aria Aug 05 '20 at 07:02
You can't hide the syntax in macros. You still have the wrong parentheses. My answer was for \ifnum anyway, rather than \ifthenelse. There may be other options with "expl" syntax. – Donald Arseneau Aug 05 '20 at 09:37

score 1 · Answer 3 · answered Aug 06 '20 at 09:12

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{math}
\begin{document}
\begin{tikzpicture}
\foreach \x in {1,...,4} {
\tikzmath {\xEnd=\x+1;}
\foreach \y in {1,...,\xEnd} {
\fill[red!50] (\x,\y) 
ellipse [x radius=3pt, y radius=6pt, rotate={ifthenelse(\x==1 || \x==2 && \y==1,0,-45)}];
}}
\draw [|-|] (.895,1) -- ++(0.211,0);
\end{tikzpicture}
\end{document}

score 0 · Answer 4 · answered Aug 06 '20 at 02:34

Found a much simpler solution. Below are the key ideas:

\ifthenelse from ifthen package in CTAN is that powerful conditional command.
\ifthenelse{<test>}{<then clause>}{<else clause>}is the command format wherein <test> is a boolean expression using the infix connectives, \and, \or, the unary \not and parentheses \( \).

Also \OR and \AND are safer to be used with \ifthenelse rather than using \or and \andsince it can’t be misinterpreted when appearing inside a TEX-conditional in which \or has a different meaning. So here is the code:

\documentclass{standalone}
\usepackage{tikz,ifthen}
\begin{document}
\begin{tikzpicture}
\foreach \x in {1,...,4}
\foreach \y in {1,...,4}
{
\ifthenelse{\(\x=1 \AND \y=1\) \OR \(\x=2 \AND \y=1\) }
{\fill[red!50] (\x,\y) ellipse [x radius=3pt , y radius= 6pt, rotate=0];}
{\fill[red!50] (\x,\y) ellipse [x radius=3pt , y radius= 6pt, rotate=-45];}
\ifnum \x<\y
\breakforeach
\fi
}
 \draw [|-|] (.895,1) -- ++(0.211,0);
\end{tikzpicture}
\end{document}

On a conditional command: more powerful than \ifnum

4 Answers4