From: Martin Mares <mj@ucw.cz>
Date: Mon, 28 Jan 2008 10:43:39 +0000 (+0100)
Subject: Finished iterated Jarnik.
X-Git-Tag: printed~272
X-Git-Url: http://mj.ucw.cz/gitweb/?a=commitdiff_plain;h=b3579cbf4fc73924d2564856a79865f2bf6f6e2d;p=saga.git

Finished iterated Jarnik.
---

diff --git a/macros.tex b/macros.tex
index 3fc9efa..7877871 100644
--- a/macros.tex
+++ b/macros.tex
@@ -32,6 +32,7 @@
 \def\<#1>{\leavevmode\hbox{\it #1\/}}
 \let\>=\noindent
 \def\qed{{\parfillskip=0pt\allowbreak\hfill\nobreak $\spadesuit$\par}}
+\def\qeditem{{\parfillskip=0pt\hfill\rlap{\hskip\rightskip\llap{$\spadesuit$}}\par}}
 \def\FIXME#1{\>{\bo TODO:} #1}
 \def\symdiff{\mathbin{\Delta}}
 \def\hphantas#1#2{\setbox0=\hbox{#2}\hbox to \wd0{#1\hss}}
diff --git a/mst.tex b/mst.tex
index 64a4921..dadd2a0 100644
--- a/mst.tex
+++ b/mst.tex
@@ -992,7 +992,7 @@ contract the graph along the edges of~this forest and iterate.
 \:$m_0\=m$.
 \:While $n>1$: \cmt{We will call iterations of this loop \df{phases}.}
 \::$F\=\emptyset$. \cmt{forest built in the current phase}
-\::$t\=2^{2m_0/n}$. \cmt{the limit on the heap size}
+\::$t\=2^{2m_0/n}$. \cmt{the limit on heap size}
 \::While there is a~vertex $v_0\not\in F$:
 \:::Run the improved Jarn\'\i{}k's algorithm (\ref{jarniktwo}) from~$v_0$, stop when:
 \::::all vertices have been processed, or
@@ -1015,26 +1015,26 @@ non-indexed $G$, $m$ and~$n$ will correspond to the graph given as~input.
 However the choice of the parameter~$t$ can seem mysterious, the following
 lemma makes the reason clear:
 
-\lemma
-The $i$-th phase of the Iterated Jarn\'\i{}k's algorithm runs in time~$\O(m_i)$.
+\lemma\id{ijphase}%
+The $i$-th phase of the Iterated Jarn\'\i{}k's algorithm runs in time~$\O(m)$.
 
 \proof
 During the phase, the heap always contains at most~$t_i$ elements, so it takes
 time~$\O(\log t_i)=\O(m/n_i)$ to delete an~element from the heap. The trees~$R_i^j$
 are disjoint, so there are at most~$n_i$ \<DeleteMin>'s over the course of the phase.
 Each edge is considered at most twice (once per its endpoint), so the number
-of the other heap operations is~$\O(m_i)$. Together, it equals $\O(m_i + n_i\log t_i) = \O(m_i)$.
+of the other heap operations is~$\O(m_i)$. Together, it equals $\O(m_i + n_i\log t_i) = \O(m_i+m) = \O(m)$.
 \qed
 
 \lemma
 Unless the $i$-th phase is final, the forest~$F_i$ consists of at most $2m_i/t_i$ trees.
 
 \proof
-As every edge of~$G_i$ is incident with at most two such trees, it is sufficient
+As every edge of~$G_i$ is incident with at most two trees of~$F_i$, it is sufficient
 to establish that there are at least~$t_i$ edges incident with the vertices of every
 such tree~(*).
 
-The forest~$F_i$ evolves by additions of the trees~$R_i^j$. There are three possibilities
+The forest~$F_i$ evolves by additions of the trees~$R_i^j$. Let us consider the possibilities
 how the algorithm could have stopped growing the tree~$R_i^j$:
 \itemize\ibull
 \:the heap had more than~$t_i$ elements (step~10): since the elements stored in the heap correspond
@@ -1045,9 +1045,8 @@ how the algorithm could have stopped growing the tree~$R_i^j$:
   instead of edges incident with the tree itself, because we needed the tree edges
   to be counted as well.}
 \:all vertices have been processed (step~8): this can happen only in the final phase.
+\qeditem
 \endlist
-\>In all three cases, there are sufficiently many incident edges.
-\qed
 
 \thm\id{itjarthm}%
 The Iterated Jarn\'\i{}k's algorithm finds the MST of the input graph in time
@@ -1064,14 +1063,15 @@ of~$G_{i+1}$ correspond to the components of~$F_i$, by the previous lemma $n_{i+
 2m_i/t_i$. Then $t_{i+1} = 2^{2m/n_{i+1}} \ge 2^{2m/(2m_i/t_i)} = 2^{(m/m_i)\cdot t_i} \ge 2^{t_i}$,
 therefore:
 $$
-t_i \ge 2^{2^{2^{\vdots^{m/n}}}}
+\left. \vcenter{\hbox{$\displaystyle t_i \ge 2^{2^{\scriptstyle 2^{\scriptstyle\vdots^{\scriptstyle m/n}}}} $}}\;\right\}
+\,\hbox{a~tower of~$i$ exponentials.}
 $$
-and as soon as~$t_i\ge n$, the $i$-th phase must be final, because at that time
-there is enough space in the heap to process the whole graph.
+As soon as~$t_i\ge n$, the $i$-th phase must be final, because at that time
+there is enough space in the heap to process the whole graph. So~there are
+at most~$\beta(m,n)$ phases and we already know (Lemma~\ref{ijphase}) that each
+phase runs in linear time.
 \qed
 
-\FIXME{The notation is clumsy and so is the proof, at least typographically.}
-
 \cor
 The Iterated Jarn\'\i{}k's algorithm runs in time $\O(m\log^* n)$.
 
@@ -1082,6 +1082,7 @@ $\beta(m,n) \le \beta(1,n) = \log^* n$.
 
 
 
+
 % use \para
 % G has to be connected, so m=O(n)
 % mention Steiner trees