Document cartesian() operation

core/src/main/scala/spark/RDD.scala

@@ -243,6 +243,10 @@ abstract class RDD[T: ClassManifest](@transient sc: SparkContext) extends Serial
    */
   def glom(): RDD[Array[T]] = new GlommedRDD(this)
 
+  /**
+   * Return the Cartesian product of this RDD and another one, that is, the RDD of all pairs of
+   * elements (a, b) where a is in `this` and b is in `other`.
+   */
   def cartesian[U: ClassManifest](other: RDD[U]): RDD[(T, U)] = new CartesianRDD(sc, this, other)
 
   /**

core/src/main/scala/spark/api/java/JavaRDDLike.scala

@@ -123,6 +123,10 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
   def glom(): JavaRDD[JList[T]] =
     new JavaRDD(rdd.glom().map(x => new java.util.ArrayList[T](x.toSeq)))
 
+  /**
+   * Return the Cartesian product of this RDD and another one, that is, the RDD of all pairs of
+   * elements (a, b) where a is in `this` and b is in `other`.
+   */
   def cartesian[U](other: JavaRDDLike[U, _]): JavaPairRDD[T, U] =
     JavaPairRDD.fromRDD(rdd.cartesian(other.rdd)(other.classManifest))(classManifest,
       other.classManifest)