[Latex] Algorithm

1. algorithm and algorithmic

1.1 Adding packages

\usepackage{algorithm}
\usepackage{algorithmic}

1.2 Examples of algorithm

\begin{algorithm}[htb]         % begin the algorithm environment
\caption{This is an algorithm} % name of the algorithm
\label{algorithm:alg1}         % give it a label for referencing
\begin{algorithmic}            % begin an algorithm
\REQUIRE something input       % input of an algorithm
\STATE set some initial value   
\FOR {condition for}           % for loop begins
\STATE do something for
\ENDFOR                        % end for loop
\REPEAT                        % repeat loop
\STATE do something repeat
\UNTIL {condition repeat}      % end repeat loop
\IF {condition if}             % if condition begins
\STATE do something if
\ELSE 
\STATE do something else
\ENDIF                         % end if
\WHILE {condition while}       % while loop
\STATE do something while 
\ENDWHILE                      % end while loop
\RETURN $S$                    % return final result
\end{algorithmic}              % end an algorithm
\end{algorithm}                % end the algorithm environment

result

If you want to replace require and return with input and output, you need to add two lines

\renewcommand{\algorithmicrequire}{ \textbf{Input:}} %Use Input in the format of Algorithm
\renewcommand{\algorithmicreturn}{ \textbf{Output:}} %UseOutput in the format of Algorithm

2. algorithm2e

2.1 Adding package

\usepackage[linesnumbered,boxed]{algorithm2e}

2.2 Example

\begin{algorithm}
%\SetAlgoNoLine
\caption{This is an algorithm}
\KwIn {Input}  %knote that Kw for key words
\KwData{data for alforithm: same as input}
\KwOut {Output}
\KwResult{same for output}
initialization\;
\For{for loop}{
 do something for
}
\While{while loop}{
 do something while\;
}
\If{condition if}{
 do something if\;
}
\eIf{condition if else}{
 do something if\;
}{
 do other thing\;
}
\end{algorithm}  

result

Note useful option for algorithm2e

% 1.boxed: to have algorithms enclosed in a box.
% 2.boxruled: surround algorithm by a box, puts caption above and add a line after caption.
% 3.ruled: to have algorithms with a line at the top and the bottom. Note that the caption is not
% centered under the algorithm anymore but is set at the beginning of the algorithm
% 4.algoruled: as above but with extra spaces after the rules
% 5.tworuled: tworuled acts like ruled but doesn’t put a line after the title.
% 6.plain: the default, with no feature.

% 1.algochapter: algorithms are numbered within chapter numbers.
% 2.algosection: (default) algorithms are numbered within section numbers.
% 3.algopart: algorithms are numbered within part numbers.
% 4.procnumbered: makes the procedure and function to be numbered as algorithm.

useful
http://tug.ctan.org/tex-archive/macros/latex/contrib/algorithm2e/doc/algorithm2e.pdf