alignamsmathstarred-version
After some brief searching I can't find the difference between align and align*. Google summarily ignoring the * is making it harder I think.
Can you tell me the difference between these two?
Moreover, can you tell me where you generally go for this type of information? As a relatively new user I'm still building up my resources.
A bit of background first. When Knuth wrote TeX, he realised that most macros would not need to absorb more than one paragraph as an argument. As a result, a good way to test for errors such as a missing } is to forbid macros to accept paragraph tokens (either those generated by blank lines or explicit \par tokens). So he created \def for definitions which cannot take a paragraph token, and the \long prefix to allow them to:
\def\examplea#1{% #1 cannot contain \par
}
\long\def\exampleb#1{% #1 can contain \par
}
When LaTeX was written, Lamport created \newcommand as a wrapper around \def with various bits of error checking. He found that paragraph tokens can pop up in odd places. So he decided that \newcommand would be 'long'. When the LaTeX team took over for LaTeX2e, they decided that you would need to add the modifier * to prevent this:
\newcommand{\examplea}[1]{% #1 can contain \par
}
\newcommand*{\exampleb}[1]{% #1 cannot contain \par
}
Most of the time, \newcommand* is the best choice as you want the error-checking that it provides. That is why examples given by experienced LaTeX users normally use this form, rather than just \newcommand.
The same behaviour is seen with \newenvironment:
\newenvironment{examplea}[1]{% #1 can contain \par
}{}
\newenvironment*{exampleb}[1]{% #1 cannot contain \par
}{}
This works by defining \examplea and \endexamplea more-or-less using \newcommand, and \exampleb and \endexampleb more-or-less using \newcommand*. As a result, the 'end' macros have the same 'long' status as the 'begin' ones, even though they never take arguments. (Note that this does not affect what can go into the body of the environment, only the arguments at the start.) Environments are covered in more detail in What is the difference between \newenvironment and \newenvironment*?.
For LaTeX3, we've decided to take a somewhat hybrid approach. If you use xparse for defining document commands, they are only 'long' if you ask for it:
\NewDocumentCommand\examplea{m}{% #1 cannot contain \par
}
\NewDocumentCommand\examplab{+m}{% #1 can contain \par
}
(We've decided on + to represent a long argument). On the other hand, for internal use it is normally best to accept paragraph tokens, and to leave the filtering to the user interface level.
There are many differences. The main one is in the fact that \mathrm{xyz} behaves like an ordinary letter, while \operatorname{xyz} behaves like function names such as \sin. Here's an illustration
$\sin x + \sin(x+y) + a\sin z$
$\mathrm{sin} x + \mathrm{sin}(x+y) + a\mathrm{sin}z$
where it's clear that the second line is typeset wrong. Even if your "operator" requires parentheses after it, it should be \operatorname, as the third summand shows, where a thin space separates the coefficient from the operator.
Another subtle difference is in how some characters are interpreted in \mathrm and in \operatorname. Suppose you have an operator to be called "pre-norm", with a hyphen. Here's the example
$\operatorname{pre-norm}(\mathbf{v})$
$\mathrm{pre-norm}(\mathbf{v})$
and now it's clear what is to be used. Indeed \operatorname (and the same holds for macros defined with \DeclareMathOperator) treats punctuation symbols in a special way; \mathrm, instead, treats them as math symbols.
Best Answer
The star at the end of the name of a displayed math environment causes that the formula lines won't be numbered. Otherwise they would automatically get a number.
You can read about that in the amsmath user's guide since
alignbelongs to amsmath.Such information can usually be found in the package documentation. Type
texdoc packagenameat the command prompt or visit http://ctan.org/pkg/packagename. If you use google or another search engine, look for starred and commandname.Commonly, a star symbol
*means a version of a command that behaves differently from the original. That often means suppressing numbering but could also refer to special features. For example, have a look at What's the difference between\newcommandand\newcommand*?