Add an optimized dotProduct to OpenMapRealVector.

Slightly modified from contribution by Jake Mannix.
JIRA: MATH-317


git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@890159 13f79535-47bb-0310-9956-ffa450edef68

src/main/java/org/apache/commons/math/linear/AbstractRealVector.java

@@ -196,7 +196,7 @@ public abstract class AbstractRealVector implements RealVector {
     public double getDistance(RealVector v) throws IllegalArgumentException {
         checkVectorDimensions(v);
         double d = 0;
-        Iterator<Entry> it = sparseIterator();
+        Iterator<Entry> it = iterator();
         Entry e;
         while (it.hasNext() && (e = it.next()) != null) {
             final double diff = e.getValue() - v.getEntry(e.getIndex());
@@ -207,15 +207,7 @@ public abstract class AbstractRealVector implements RealVector {
 
     /** {@inheritDoc} */
     public double getDistance(double[] v) throws IllegalArgumentException {
-        checkVectorDimensions(v.length);
-        double d = 0;
-        Iterator<Entry> it = iterator();
-        Entry e;
-        while (it.hasNext() && (e = it.next()) != null) {
-            final double diff = e.getValue() - v[e.getIndex()];
-            d += diff * diff;
-        }
-        return Math.sqrt(d);
+        return getDistance(new ArrayRealVector(v,false));
     }
 
     /** {@inheritDoc} */

src/main/java/org/apache/commons/math/linear/OpenMapRealVector.java

@@ -303,6 +303,34 @@ public class OpenMapRealVector extends AbstractRealVector implements SparseRealV
         return new OpenMapRealVector(this);
     }
 
+    /**
+     * Optimized method to compute the dot product with an OpenMapRealVector.
+     * Iterates over the smaller of the two.
+     * @param v The vector to compute the dot product with
+     * @return The dot product of <code>this</code> and <code>v</code>
+     * @throws IllegalArgumentException If the dimensions don't match
+     */
+    public double dotProduct(OpenMapRealVector v) throws IllegalArgumentException {
+        checkVectorDimensions(v.getDimension());
+        boolean thisIsSmaller  = entries.size() < v.entries.size();
+        Iterator iter = thisIsSmaller  ? entries.iterator() : v.entries.iterator();
+        OpenIntToDoubleHashMap larger = thisIsSmaller  ? v.entries : entries;
+        double d = 0;
+        while(iter.hasNext()) {
+            iter.advance();
+            d += iter.value() * larger.get(iter.key());
+        }
+        return d;
+    }
+    
+    /** {@inheritDoc} */
+    public double dotProduct(RealVector v) throws IllegalArgumentException {
+        if(v instanceof OpenMapRealVector) {
+            return dotProduct((OpenMapRealVector)v);
+        } else {
+            return super.dotProduct(v);
+        }
+    }
 
     /** {@inheritDoc} */
     public OpenMapRealVector ebeDivide(RealVector v) throws IllegalArgumentException {