## LaTeX forum ⇒ Math & Science ⇒ numerical conditions

Information and discussion about LaTeX's math and science related features (e.g. formulas, graphs).
kent
Posts: 28
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: 198
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: 28
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: 8460
Joined: Mon Mar 10, 2008 9:44 pm
Location: Hamburg, Germany
Contact:
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