## LaTeX forum ⇒ Math & Science ⇒ numerical conditions Topic is solved

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kent
Posts: 45
Joined: Thu Oct 20, 2016 3:41 pm

### numerical conditions

I often should have liked to be able to test for numerical conditions in my PGF macros.
Let me illustrate with one simple example:
Let A and B be two given poinst where we have access to their coordinates, say A = (\xA,\yA) and B = (\xB,\yB).
I would then like to be able to check if A = B within some tolerance.
But how should I test to see, say, for \dx = \xB-\xA that abs(\dx) < \eps for a small defined value of \eps (i.e 0.0005)?
As far as I know the Latex \ifthenelse cannot be used.
Kent Holing, NORWAY

mas
Posts: 206
Joined: Thu Dec 04, 2008 4:39 am
Looking at the pgf manual, Section 90, you can see that there is a pgfmath library which has commands to do what you need. I am just pasting below from the manual (page 939):
90.2
Comparison and logical functions
In addition to the commands described in Section 89.3.5, the following command was provided by Christian
Feuersänger:
\pgfmathapproxequalto{<x>}{<y>}
Defines \pgfmathresult 1.0 if |<x>−<y>|< 0.0001, but 0.0 otherwise. As a side-effect, the global boolean
\ifpgfmathcomparison will be set accordingly.

OS: Debian/GNU Linux; LaTeX System : TeXLive; Editor : Vim

kent
Posts: 45
Joined: Thu Oct 20, 2016 3:41 pm
Thanks, I see I need to upgrade the PGF version I am using or could anybody supply the code needed/mentioned?

Stefan Kottwitz
Posts: 8955
Joined: Mon Mar 10, 2008 9:44 pm
Hi Kent!

It's probably good to update in any case. I remember you worked on an intersection topic, that also was solvable with PGF 3 aka TikZ 3. It provides a lot more features than PGF 2. Otherwise you may re-program already existing new features.

You may consider to update the whole TeX installation. LaTeX evolves, new features, packages, and bug fixes appear.

Stefan

kent
Posts: 45
Joined: Thu Oct 20, 2016 3:41 pm
Since I recently got PGF 3.0 installed, I like to revisit the above.
What's wrong with the if statement below?
\pgfmathapproxequalto{0.15}{0.1499999999};\let\out\pgfmathresult;%here \out is 1.0 as it should\ifthenelse{\ifpgfmathcomparison}{true}{false};%here I thought I should get true% since I thought \ifpgfmathcomparison is true since \out is 1.0

Kent

kent
Posts: 45
Joined: Thu Oct 20, 2016 3:41 pm
By using \let\outt\pgfmathint{\out} I transformed 1.0 to 1 and I could then use \ifthenelse{\outt>0} etc..
But, I still wonder how to use the boolean \ifpgfmathcomparison.

cgnieder
Site Moderator
Posts: 1988
Joined: Sat Apr 16, 2011 7:27 pm
\ifpgfmathcomparison can be checked like any boolean defined with \newif:

\documentclass{article} \usepackage{tikz,etoolbox,ifthen} \begin{document} \pgfmathapproxequalto{0.15}{0.1499999999} % standard TeX:\ifpgfmathcomparison  true%\else  false%\fi % etoolbox:\ifbool{pgfmathcomparison}{true}{false} % ifthen:\ifthenelse{\boolean{pgfmathcomparison}}{true}{false} \end{document}
Clemens
------------------------------
chemmacros · chemformula · leadsheets · xsim

kent
Posts: 45
Joined: Thu Oct 20, 2016 3:41 pm
One more question, how do I compare numerically numbers in if statements such that
if(2.3>5.7}{false}{true}?

kent
Posts: 45
Joined: Thu Oct 20, 2016 3:41 pm
Reading the manuals more carefully, I managed to resolve myself. Sorry, for bothering you with this.