# [texhax] Help on cross-references

Christian H. Aastrup c at aastrup.org
Fri Mar 13 23:03:17 CET 2009

Hi Bob and everyone

You've understood exactly what I'm looking for and perhaps you've explained better.

I sure hope that someone out there knows how to implement this.

- Christian
----- Original Message -----
From: Robert Wilson
To: Tom Schneider
Cc: texhax ; Christian H. Aastrup
Sent: Friday, March 13, 2009 9:42 PM
Subject: Re: [texhax] Help on cross-references

What Christian wants (I believe) is for Equations to be labeled as (1), (2), ..., and within the same section in which they are first displayed, they would be referred to as Equation (1), etc. When referring to Equations in a different section, but in the same chapter, it would display Equation (1.2) for the second equation in the first section. When referring to equations in a different chapter, it would display Equation (1.2.3) for the third equation in the second section of the first chapter.

Although I'm out of my league here, I envision a solution wherein you redefine the \theequation command, and use the ifthen package to exame the \section and \chapter of the current location, compare with the location of the equation, and display different results accordingly. Something like:

\def\theequation {%
\ifthenelse{ \equal{\chapter}{\Eq_chapter} }% If same chapter
{\ifthenelse{ \equal{\section}{\Eq_section} }% and same section
{\equation}% print just the number.
{\Eq_section.\equation}% If different section, print section number as well
}% If different chapter, print the chapter and section numbers
{\Eq_chapter.\Eq_section.\equation} }

Hopefully I closed all my brackets. The only thing that you're missing now is how to figure out in what chapter/section an equation begins (I made up the commands \Eq_chapter and \Eq_section). Hopefully someone else can post that information.

Cheers,
Bob Wilson

On Fri, Mar 13, 2009 at 1:10 PM, Tom Schneider <toms at ncifcrf.gov> wrote:

Christian:

> Chapter 1
>
> text text text text
> text text text text
>
> Section 1
>
> An equation
>
> 2+2 < 5                (1)
>
> A reference to the equation
> now looks like: (1)
>
> Section 2
>
> text text text text
> text text text text
>
> A ref to the equation
> is now (1.1)

This probably would give some readers a bit of confusion since the
notation has changed.  I would design it to have the first reference
be (1.1) [section.equation] in all cases.

> Chapter 2
>
> text text text text
> text text text text
>
> A ref to the equation
> is now (1.1.1)

At this point I'm completely confused.  The third time one
would cite it as (1.1.1.1) and the fourth time (1.1.1.1.1)?

(I'll let others say how to do these things technically.)

Tom

Dr. Thomas D. Schneider
National Institutes of Health
National Cancer Institute
Center for Cancer Research Nanobiology Program
Molecular Information Theory Group
Frederick, Maryland  21702-1201
toms at ncifcrf.gov
permanent email: toms at alum.mit.edu
http://www.ccrnp.ncifcrf.gov/~toms/
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