diff -u -r1.2 -r1.3
--- HPSEcal.java	17 May 2011 23:10:46 -0000	1.2
+++ HPSEcal.java	25 May 2011 20:55:09 -0000	1.3
@@ -1,7 +1,9 @@

 package org.lcsim.geometry.subdetector;
 
 import java.util.Comparator;

+import java.util.HashMap;

 import java.util.HashSet;

+import java.util.Map;

 import java.util.Set;
 
 import org.jdom.Element;

@@ -10,7 +12,9 @@

 import org.lcsim.geometry.util.IDEncoder;
 
 /**

- * @author jeremym

+ * Reconstruction version of HPS ECal with crystal array.
+ * 
+ * @author Jeremy McCormick <[log in to unmask]>

  */
 public class HPSEcal extends AbstractSubdetector
 {

@@ -19,6 +23,7 @@

     private double beamgap;
     private double dface;
     private boolean oddX;

+    private HashMap<Long,Set<Long>> neighborsMap = null;

     
     HPSEcal(Element node) throws JDOMException
     {

@@ -255,4 +260,46 @@

     {
         return ny;
     }   

+    
+    /**
+     * Create a map of crystal IDs to the <code>Set</code> of neighbor crystal IDs.
+     * @return A map of neighbors for each crystal ID.
+     */
+    public Map<Long,Set<Long>> makeNeighborsMap()
+    {
+        Map<Long,Set<Long>> neighborsMap = new HashMap<Long,Set<Long>>();
+        
+        IDDecoder dec = getIDDecoder();
+        IDEncoder enc = new IDEncoder(dec.getIDDescription());
+        
+        int nfields = dec.getFieldCount();
+        int[] vals = new int[nfields];
+
+        vals[dec.getFieldIndex("system")] = getSystemID();
+        
+        int idxx = dec.getFieldIndex("ix");
+        int idxy = dec.getFieldIndex("iy");
+                
+        for (int side=-1; side <=1; side++)
+        {
+            vals[dec.getFieldIndex("side")] = side;
+            if (side == 0) continue;
+            for (int iy=1; iy<=ny; iy++)
+            {
+                for (int ix=0; ix<=nx; ix++)
+                {                             
+                    vals[idxx] = ix;
+                    vals[idxy] = iy;
+                    
+                    Long id = enc.setValues(vals);
+
+                    Set<Long> neighbors = getNeighbors(id);
+                    
+                    neighborsMap.put(id, neighbors);
+                }
+            }
+        }
+        
+        return neighborsMap;
+    }

 }

\ No newline at end of file