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+\documentclass[11pt,fullpage]{article}
+\usepackage[urlcolor=blue,colorlinks=true]{hyperref}
+
+\oddsidemargin 0.0in
+\textwidth 6.5in
+
+\begin{document}
+
+\title{Getting Started with the Genome Analysis Toolkit (GATK)}
+\author{Matt Hanna}
+\date{16 Mar 2009}
+\maketitle
+
+\section{Build Prerequisites}
+GATK requires JDK 1.6 and Ant 1.7.1 to compile.
+
+\section{Getting and Building the Source}
+GATK is located in the Sting svn repository, and
+compiles using a build.xml in the root directory.
+
+Download and build the source as follows:
+\begin{verbatim}
+  svn co https://svnrepos/Sting/trunk Sting
+  cd Sting
+  ant
+\end{verbatim}
+
+\section{Getting Started}
+The core concept behind GATK is the walker, a class that implements the 
+three core operations, filtering, mapping, and reducing.
+
+\begin{description}
+  \item [filter] reduces the size of the dataset by applying a predicate.  
+  \item [map] Applies a function to each individual element in a dataset, 
+    effectively 'mapping' it to a new element.
+  \item [reduce] Inductively combines the elements of a list.  The base
+    case is supplied by the reduceInit() function, and the inductive step
+    is performed by the reduce() function.
+\end{description}
+Users of the GATK will provide a walker to run their analyses.  The engine
+will produce a result by first filtering the dataset, running a map operation,
+and finally reducing the map operation to a single result.  
+
+\section{Example}
+This walker will print output for each read it sees, eventually computing the
+total number of reads by mapping every read to 1 and summing all the 1s to
+realize the total number of reads.
+
+\begin{verbatim}
+import net.sf.samtools.SAMRecord;
+
+import org.broadinstitute.sting.gatk.LocusContext;
+import org.broadinstitute.sting.gatk.walkers.BasicReadWalker;
+
+/**
+ * Define a class extending from BasicReadWalker with types
+ * <MapType,ReduceType>.  
+ */
+public class HelloWalker extends BasicReadWalker<Integer,Long> {
+    private Long currentRead = 0L;
+
+    // Maps each read to the value 1.
+    public Integer map(LocusContext context, SAMRecord read) {
+        System.out.printf("Hello read %d%n", ++currentRead );
+        return 1; 
+    }
+
+    // Provides an initial value for the reduce function.
+    public Long reduceInit() { return 0L; }
+    
+    // Defines how to compute the reduction given a value in the list. 
+    public Long reduce(Integer value, Long sum) { 
+        return sum + value;
+    }
+}
+\end{verbatim}
+To compile the walker:
+\begin{verbatim}
+setenv CLASSPATH $STING_HOME/dist/GenomeAnalysisTK.jar:$STING_HOME/dist/sam-1.0.jar
+javac HelloWalker.java
+\end{verbatim}
+To run the walker:
+\begin{verbatim}
+mkdir $STING_HOME/dist/walkers
+cp HelloWalker.java $STING_HOME/dist/walkers
+java -Xmx4096m -jar dist/GenomeAnalysisTK.jar \
+     INPUT_FILE=/broad/1KG/legacy_data/trio/na12878.bam \
+     ANALYSIS_NAME=Hello L=chr1:10000000-10000100
+\end{verbatim}
+This command will run the walker across a subsection of chromosome 1, operating on 
+reads which align to that subsection.  
+
+\end{document}