\chapter{Section alignment}

\section{Needleman - Wunsch algorithm}

\begin{algorithm}
	\caption{Needleman-Wunsch Algorithm}
	\begin{algorithmic}[1]
		\Procedure{FillMatrix}{$S_{1}$: Array($m$), $S_{2}$: Array($n$)}
		\Comment{$sub(a, b)$ is the substitution score, $del(a)$ and $ins(a)$ are the deletion and insertion penalty, in regard with the reference $S_{1}$ sequence}
		\State $M = $ Array($m+1$, $n+1$)
		\Comment{Initialize the matrix first column and first row}
		\State $P = $ Array($m$, $n$) \Comment{Store the direction of the cell we chose to build the next cell up on.}
		\For {($i = 0$; $i < m+1$; $i++$)}
		\State $M[i][0] = i * del(S_{1}[i])$
		\EndFor
		\For {($j = 0$; $j < n+1$; $j++$)}
		\State $M[0][j] = j * ins(S_{2}[j])$
		\EndFor
		\Comment{Fill the remaining matrix}
		\For {($i = 1$; $i < m+1$; $i++$)}
		\For {($j = 1$; $j < n+1$; $j++$)}
		\State $delete = M[i-1][j] + del(S_{1}[i-1])$
		\State $insert = M[i][j-1] + ins(S_{2}[j-1])$
		\State $substitute = M[i-1][j-1] + sub(S_{1}[i-1], S_{2}[j-1])$
		\State $choice = \max \{delete, insert, substitute\}$
		\If {$substitute = choice$}
		\State $P[i-1][j-1] = '\nwarrow'$
		\ElsIf {$insertion = choice$}
		\State $P[i-1][j-1] = '\uparrow'$
		\Else
		\State $P[i-1][j-1] = '\leftarrow'$
		\EndIf
		\State $M[i][j] = choice$
		\EndFor
		\EndFor
		\EndProcedure
		\Procedure{ShowAlignment}{$S_{1}$: Array($m$), $S_{2}$: Array($n$)}
		\State $extend_{1} = ''$
		\State $extend_{2} = ''$
		\State $i = m$
		\State $j = n$
		\While{$i > 0$ and $j > 0$}
		\If {$P[i-1][j-1] = '\nwarrow'$}
		\State $extend_{1} = S_{1}[i-1] \circ extend_{1}$
		\State $extend_{2} = S_{2}[j-1] \circ extend_{2}$
		\State $i--$
		\State $j--$
		\ElsIf {$P[i-1][j-1] = '\uparrow'$}
		\State $extend_{1} = S_{1}[i-1] \circ extend_{1}$
		\State $extend_{2} =\quad '-' \circ extend_{2}$
		\State $i--$
		\Else
		\State $extend_{1} =\quad '-' \circ extend_{1}$
		\State $extend_{2} = S_{2}[j-1] \circ extend_{2}$
		\State $j--$
		\EndIf
		\EndWhile
		\State \Call{print}{$extend_{1}$}
		\State \Call{print}{$extend_{2}$}
		\EndProcedure
		\State \Call{FillMatrix}{$S_{1}$, $S_{2}$}
		\State \Call ShowAlignment($S_{1}$, $S_{2}$)
	\end{algorithmic}
\end{algorithm}