Math & Science ⇒ Equation not centered

[localghost]

Since this is the common way to go, his solution is absolutely reliable. Nothing to be afraid of. Your machine won't blow up.

[cgnieder]

You can replace this with

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\numberwithin{equation}{section}

It has the same effect.

Hmmm, yes. But I must admit that I'm pretty nervous about modifying my preamble, because my document is now so large and complex, I don't want to mess with this huge castle of cards.

Changing just a single line of code in the preamble may have HUGE consequences on the whole document.

Well, you don't have to but if you look at the definition of \numberwithin you'll see that it does exactly the same except for checking if the counters exist.

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\newcommand{\numberwithin}[3][\arabic]{%
  \@ifundefined{c@#2}{\@nocounterr{#2}}{%
    \@ifundefined{c@#3}{\@nocnterr{#3}}{%
      \@addtoreset{#2}{#3}%
      \@xp\xdef\csname the#2\endcsname{%
        \@xp\@nx\csname the#3\endcsname .\@nx#1{#2}}}}%
}

\@xp is an alias for \expandafter and \@nx another one for \noexpand.

Regards

[Cham]

that it does exactly the same except for checking if the counters exist.

Hmm, this is what makes me a bit nervous. What does this implies ?

I don't think this should be a concern in my case, but...

[cgnieder]

If you use \numberwithin{equation}{section} it checks for the counters equation and section. Since both exist nothing happens. But as I said: you don't have to replace your code. Since it is the same it really doesn't matter.

Regards

[Cham]

Ok, thanks a lot for your help guys, it's really appreciated.

I consider my issue solved.

EDIT : Hmmm, not exactly. There's still a glitch, described in my next message below...

[Cham]

Guys, I noticed a small glitch with the previous solution. Here's again the code example which solves my previous issue, but notice the small indent there's on the first text line just after the first equation. There shoulnd't be any indent there.

Adding \noindent doesn't do anything.

What is happening here ?

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\documentclass{book}
\usepackage{mathtools}
\usepackage{tensor}

\newtagform{nospace}[\llap\bgroup(]{}{\egroup)}

\numberwithin{equation}{section}

\usepackage[nopar]{lipsum}% for dummy text
\begin{document}
\chapter{Blah}
\section{Blub}

\lipsum[4]
\usetagform{nospace}
\begin{equation}
  \frac{d^2 \, \displaystyle{\tensor{x}{^{\lambda}}}}{d\, \sigma^2} +
  \Gamma_{\mu \nu}^{\lambda} \; \frac{d\, \displaystyle{\tensor{x}{^{\mu}}}}{d\, \sigma} \,
  \frac{d\, \displaystyle{\tensor{x}{^{\nu}}}}{d\, \sigma} =
  \frac{d\, \displaystyle{\tensor{x}{^{\lambda}}}}{d\, \sigma} \,
  \frac{d\, }{d\, \sigma} \, \ln \sqrt{\, \tensor{g}{_{\mu \nu}} \;
  \frac{d\, \displaystyle{\tensor{x}{^{\mu}}}}{d\, \sigma} \,
  \frac{d\, \displaystyle{\tensor{x}{^{\nu}}}}{d\, \sigma}}.
\end{equation}
\usetagform{default}
\lipsum[4]
\begin{equation}
  \tensor{g}{_{\mu \nu}} \; \frac{d\, \displaystyle{\tensor{x}{^{\mu}}}}{d\, \sigma} \,
  \frac{d\, \displaystyle{\tensor{x}{^{\nu}}}}{d\, \sigma} =
  \tensor{g}{_{\mu \nu}} \; \frac{d\, \displaystyle{\tensor{x}{^{\mu}}}}{d\, \tau} \,
  \frac{d\, \displaystyle{\tensor{x}{^{\nu}}}}{d\, \tau} \,
  \Big( \, \frac{d\, \tau}{d\, \sigma} \Big)^{\! 2} \equiv
  \Big( \, \frac{d\, \tau}{d\, \sigma} \Big)^{\! 2}.
\end{equation}
\lipsum[4]

\end{document}

[cgnieder]

Try writing

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\usetagform{default}%

Notice the comment character! You might know (and if not it's good you learn now) that the end of a line is interpreted like a blank by TeX. So

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\usetagform{default}
Some text

is equivalent to

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\usetagform{default} Some text

Regards

[Cham]

Oh boy ! Thanks for that one.

Then this brings me another question, about the % at the end of the command line :

I believed that the % was used only to add some comments to the code, like this :

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\noindent % A comment about this command
Some text...

Now, apparently, there are other uses for that symbol ? Is that right ? I'm not sure I understand.

[cgnieder]

Well, the comment char tells TeX to ignore the rest of the line beginning with the comment char itself. This is of course quite handy to add information to the source that's not supposed to be part of the actual document. It can however also be used to hide the and of a line. When TeX finds the end of a line it actually finds the “end of line char” which is the converted into a space (or in case an empty line follows the end of the line a \par token is inserted). This is why

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\usetagform{default}%
Some text

is the same as

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\usetagform{default}Some text

but

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\usetagform{default}
Some text

is the same as

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\usetagform{default} Some text

and

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\usetagform{default}

Some text

is the same as

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\usetagform{default}\par Some text

Regards

[Cham]

Ok, thanks. This is now perfectly clear.

The case is now fully solved.