[SPARK-3974] Block Matrix Abstractions ready

Author: Burak Yavuz

mllib/src/main/scala/org/apache/spark/mllib/linalg/distributed/BlockMatrix.scala

@@ -20,18 +20,32 @@ package org.apache.spark.mllib.linalg.distributed
 import breeze.linalg.{DenseMatrix => BDM}
 
 import org.apache.spark._
-import org.apache.spark.mllib.linalg.{DenseMatrix, Matrices }
+import org.apache.spark.mllib.linalg.DenseMatrix
 import org.apache.spark.rdd.RDD
 import org.apache.spark.SparkContext._
 import org.apache.spark.storage.StorageLevel
 import org.apache.spark.util.Utils
 
-case class BlockPartition(
-    blockIdRow: Int,
-    blockIdCol: Int,
-    mat: DenseMatrix) extends Serializable
+/**
+ * Represents a local matrix that makes up one block of a distributed BlockMatrix
+ *
+ * @param blockIdRow The row index of this block
+ * @param blockIdCol The column index of this block
+ * @param mat The underlying local matrix
+ */
+case class BlockPartition(blockIdRow: Int, blockIdCol: Int, mat: DenseMatrix) extends Serializable
 
-// Information about BlockMatrix maintained on the driver
+/**
+ * Information about the BlockMatrix maintained on the driver
+ *
+ * @param partitionId The id of the partition the block is found in
+ * @param blockIdRow The row index of this block
+ * @param blockIdCol The column index of this block
+ * @param startRow The starting row index with respect to the distributed BlockMatrix
+ * @param numRows The number of rows in this block
+ * @param startCol The starting column index with respect to the distributed BlockMatrix
+ * @param numCols The number of columns in this block
+ */
 case class BlockPartitionInfo(
     partitionId: Int,
     blockIdRow: Int,
@@ -41,6 +55,13 @@ case class BlockPartitionInfo(
     startCol: Long,
     numCols: Int) extends Serializable
 
+/**
+ * A partitioner that decides how the matrix is distributed in the cluster
+ *
+ * @param numPartitions Number of partitions
+ * @param rowPerBlock Number of rows that make up each block.
+ * @param colPerBlock Number of columns that make up each block.
+ */
 abstract class BlockMatrixPartitioner(
     override val numPartitions: Int,
     val rowPerBlock: Int,
@@ -52,6 +73,14 @@ abstract class BlockMatrixPartitioner(
   }
 }
 
+/**
+ * A grid partitioner, which stores every block in a separate partition.
+ *
+ * @param numRowBlocks Number of blocks that form the rows of the matrix.
+ * @param numColBlocks Number of blocks that form the columns of the matrix.
+ * @param rowPerBlock Number of rows that make up each block.
+ * @param colPerBlock Number of columns that make up each block.
+ */
 class GridPartitioner(
     val numRowBlocks: Int,
     val numColBlocks: Int,
@@ -74,6 +103,14 @@ class GridPartitioner(
   }
 }
 
+/**
+ * A specialized partitioner that stores all blocks in the same row in just one partition.
+ *
+ * @param numPartitions Number of partitions. Should be set as the number of blocks that form
+ *                      the rows of the matrix.
+ * @param rowPerBlock Number of rows that make up each block.
+ * @param colPerBlock Number of columns that make up each block.
+ */
 class RowBasedPartitioner(
     override val numPartitions: Int,
     override val rowPerBlock: Int,
@@ -93,6 +130,14 @@ class RowBasedPartitioner(
   }
 }
 
+/**
+ * A specialized partitioner that stores all blocks in the same column in just one partition.
+ *
+ * @param numPartitions Number of partitions. Should be set as the number of blocks that form
+ *                      the columns of the matrix.
+ * @param rowPerBlock Number of rows that make up each block.
+ * @param colPerBlock Number of columns that make up each block.
+ */
 class ColumnBasedPartitioner(
     override val numPartitions: Int,
     override val rowPerBlock: Int,
@@ -114,39 +159,44 @@ class ColumnBasedPartitioner(
   }
 }
 
+/**
+ * Represents a distributed matrix in blocks of local matrices.
+ *
+ * @param numRowBlocks Number of blocks that form the rows of this matrix
+ * @param numColBlocks Number of blocks that form the columns of this matrix
+ * @param rdd The RDD of BlockPartitions (local matrices) that form this matrix
+ * @param partitioner A partitioner that specifies how BlockPartitions are stored in the cluster
+ */
 class BlockMatrix(
     val numRowBlocks: Int,
     val numColBlocks: Int,
     val rdd: RDD[BlockPartition],
     val partitioner: BlockMatrixPartitioner) extends DistributedMatrix with Logging {
 
-  // We need a key-value pair RDD to partition properly
-  private var matrixRDD = rdd.map { block =>
-      partitioner match {
-        case r: RowBasedPartitioner => (block.blockIdRow, block)
-        case c: ColumnBasedPartitioner => (block.blockIdCol, block)
-        case g: GridPartitioner => (block.blockIdRow + numRowBlocks * block.blockIdCol, block)
-        case _ => throw new IllegalArgumentException("Unrecognized partitioner")
-      }
-    }
+  // A key-value pair RDD is required to partition properly
+  private var matrixRDD: RDD[(Int, BlockPartition)] = keyBy()
 
   @transient var blockInfo_ : Map[(Int, Int), BlockPartitionInfo] = null
 
-  lazy val dims: (Long, Long) = getDim
+  private lazy val dims: (Long, Long) = getDim
 
   override def numRows(): Long = dims._1
   override def numCols(): Long = dims._2
 
   if (partitioner.name.equals("column")) {
-    require(numColBlocks == partitioner.numPartitions)
+    require(numColBlocks == partitioner.numPartitions, "The number of column blocks should match" +
+      " the number of partitions of the column partitioner.")
   } else if (partitioner.name.equals("row")) {
-    require(numRowBlocks == partitioner.numPartitions)
+    require(numRowBlocks == partitioner.numPartitions, "The number of row blocks should match" +
+      " the number of partitions of the row partitioner.")
   } else if (partitioner.name.equals("grid")) {
-    require(numRowBlocks * numColBlocks == partitioner.numPartitions)
+    require(numRowBlocks * numColBlocks == partitioner.numPartitions, "The number of blocks " +
+      "should match the number of partitions of the grid partitioner.")
   } else {
     throw new IllegalArgumentException("Unrecognized partitioner.")
   }
 
+  /* Returns the dimensions of the matrix. */
   def getDim: (Long, Long) = {
     val bi = getBlockInfo
     val xDim = bi.map { x =>
@@ -194,18 +244,20 @@ class BlockMatrix(
     }.toMap
 
     blockInfo_ = blockStartRowCols.map{ case ((rowId, colId), (partId, numRow, numCol)) =>
-      ((rowId, colId), new BlockPartitionInfo(partId, rowId, colId, cumulativeRowSum(rowId), numRow,
-        cumulativeColSum(colId), numCol))
+      ((rowId, colId), new BlockPartitionInfo(partId, rowId, colId, cumulativeRowSum(rowId),
+        numRow, cumulativeColSum(colId), numCol))
     }.toMap
   }
 
+  /* Returns a map of the information of the blocks that form the distributed matrix. */
   def getBlockInfo: Map[(Int, Int), BlockPartitionInfo]  = {
     if (blockInfo_ == null) {
       calculateBlockInfo()
     }
     blockInfo_
   }
 
+  /* Returns the Frobenius Norm of the matrix */
   def normFro(): Double = {
     math.sqrt(rdd.map(lm => lm.mat.values.map(x => math.pow(x, 2)).sum).reduce(_ + _))
   }
@@ -222,8 +274,19 @@ class BlockMatrix(
     this
   }
 
+  private def keyBy(part: BlockMatrixPartitioner = partitioner): RDD[(Int, BlockPartition)] = {
+    rdd.map { block =>
+      part match {
+        case r: RowBasedPartitioner => (block.blockIdRow, block)
+        case c: ColumnBasedPartitioner => (block.blockIdCol, block)
+        case g: GridPartitioner => (block.blockIdRow + numRowBlocks * block.blockIdCol, block)
+        case _ => throw new IllegalArgumentException("Unrecognized partitioner")
+      }
+    }
+  }
+
   def repartition(part: BlockMatrixPartitioner = partitioner): DistributedMatrix = {
-    matrixRDD = matrixRDD.partitionBy(part)
+    matrixRDD = keyBy(part)
     this
   }
 
@@ -259,80 +322,4 @@ class BlockMatrix(
     val localMat = collect()
     new BDM[Double](localMat.numRows, localMat.numCols, localMat.values)
   }
-
-  def add(other: DistributedMatrix): DistributedMatrix = {
-    other match {
-      // We really need a function to check if two matrices are partitioned similarly
-      case otherBlocked: BlockMatrix =>
-        if (checkPartitioning(otherBlocked, OperationNames.add)){
-          val addedBlocks = rdd.zip(otherBlocked.rdd).map{ case (a, b) =>
-            val result = a.mat.toBreeze + b.mat.toBreeze
-            new BlockPartition(a.blockIdRow, a.blockIdCol,
-              Matrices.fromBreeze(result).asInstanceOf[DenseMatrix])
-          }
-          new BlockMatrix(numRowBlocks, numColBlocks, addedBlocks, partitioner)
-        } else {
-          throw new SparkException(
-            "Cannot add matrices with non-matching partitioners")
-        }
-      case _ =>
-        throw new IllegalArgumentException("Cannot add matrices of different types")
-    }
-  }
-
-  def multiply(other: DistributedMatrix): BlockMatrix = {
-    other match {
-      case otherBlocked: BlockMatrix =>
-        if (checkPartitioning(otherBlocked, OperationNames.multiply)){
-
-          val resultPartitioner = new GridPartitioner(numRowBlocks, otherBlocked.numColBlocks,
-            partitioner.rowPerBlock, otherBlocked.partitioner.colPerBlock)
-
-          val multiplyBlocks = matrixRDD.join(otherBlocked.matrixRDD, partitioner).
-            map { case (key, (mat1, mat2)) =>
-              val C = mat1.mat multiply mat2.mat
-              (mat1.blockIdRow + numRowBlocks * mat2.blockIdCol, C.toBreeze)
-          }.reduceByKey(resultPartitioner, (a, b) => a + b)
-
-          val newBlocks = multiplyBlocks.map{ case (index, mat) =>
-            val colId = index / numRowBlocks
-            val rowId = index - colId * numRowBlocks
-            new BlockPartition(rowId, colId, Matrices.fromBreeze(mat).asInstanceOf[DenseMatrix])
-          }
-          new BlockMatrix(numRowBlocks, otherBlocked.numColBlocks, newBlocks, resultPartitioner)
-        } else {
-          throw new SparkException(
-            "Cannot multiply matrices with non-matching partitioners")
-        }
-      case _ =>
-        throw new IllegalArgumentException("Cannot add matrices of different types")
-    }
-  }
-
-  private def checkPartitioning(other: BlockMatrix, operation: Int): Boolean = {
-    val otherPartitioner = other.partitioner
-    operation match {
-      case OperationNames.add =>
-        partitioner.equals(otherPartitioner)
-      case OperationNames.multiply =>
-        partitioner.name == "column" && otherPartitioner.name == "row" &&
-          partitioner.numPartitions == otherPartitioner.numPartitions &&
-          partitioner.colPerBlock == otherPartitioner.rowPerBlock &&
-          numColBlocks == other.numRowBlocks
-      case _ =>
-        throw new IllegalArgumentException("Unsupported operation")
-    }
-  }
-}
-
-/**
- * Maintains supported and default block matrix operation names.
- *
- * Currently supported operations: `add`, `multiply`.
- */
-private object OperationNames {
-
-  val add: Int = 1
-  val multiply: Int = 2
-
 }