align
I use the following latex code to using align environment but the formula does not appear centered.
\begin{align}
\text{$SM$}_7 \rightarrow \text{$SM$}_1 : \{K_{NG},HMAC_{K_{1}}\}_{\{encr\}K_{1}},
\end{align}
But when writing the same code in IEEE journal latex file, the formula was centered.
Can any one help me to make text within align to be centered ??
If you "hide" the tab alignment & from align, it will fail to work as expected. This is only because & is read as part of the argument to \phantom, which knowns nothing about & and its use. As such, you either have to spread the \phantom across the aligned components, or use an altogether different approach:
\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\begin{document}
\begin{align*}
a & = b + c \\
\phantom{a} & \phantom{{} = b} + c \\ % Hides some components of above line
& = d + e \\
& \phantom{{}= d} + e % Hides some components of above line
\end{align*}
\end{document}
In the above example, some components were left untouched to indicate how some spacing correction is sometimes required when using \phantom (for example, when hiding the relation =).
The reason why \phantom around an entire cases structure works is because the tab alignment character is buried within the environment where it makes sense.
If I complete your fragment to make a document
\documentclass{article}
\usepackage{amsmath}
\begin{document}
Blah blah blah, then \[\begin{align*} \label{eq1} \text{something text}
&= \frac{a}{b} \\ &= \frac{a}{c+d} \\ & \intertext{some other text, gives}
\\ \label{eq2} a &= b+c \end{align*}\]
\end{document}
then TeX produces
! Package amsmath Error: Erroneous nesting of equation structures;
(amsmath) trying to recover with `aligned'.
See the amsmath package documentation for explanation.
Type H <return> for immediate help.
...
l.7 \\ \label{eq2} a &= b+c \end{align*}
\]
?
! Package amsmath Error: Invalid use of \intertext.
See the amsmath package documentation for explanation.
Type H <return> for immediate help.
...
l.7 \\ \label{eq2} a &= b+c \end{align*}
\]
?
! Package amsmath Error: Multiple \label's: label 'eq1' will be lost.
See the amsmath package documentation for explanation.
Type H <return> for immediate help.
...
l.7 \\ \label{eq2} a &= b+c \end{align*}
\]
?
[1
After an error any typeset output that may be produced is essentially arbitrary and not really to be looked at, TeX recovers from errors only to allow further syntax checking, usually the typeset result is nonsense.
If I fix the errors reported namely align* should not be inside \[, \intertext should be at the start of the line and you shouldn't use \label as the * form is not numbered so there is nothing to reference, I get
\documentclass{article}
\usepackage{amsmath}
\begin{document}
Blah blah blah, then
\begin{align*} \text{something text}
&= \frac{a}{b} \\ &= \frac{a}{c+d} \\
\intertext{some other text, gives}
\\ a &= b+c
\end{align*}
\end{document}
which produces
Best Answer
Looking at the image I would guess you have the
fleqnoption to set math flush left which is why it is not centred butalignshould never be used for one-lien equationsshould be
or perhaps
if SM is a single identifier here not a combination of S and M