Github user chiwanpark commented on a diff in the pull request:
https://github.com/apache/flink/pull/2152#discussion_r76551085
--- Diff:
flink-libraries/flink-ml/src/main/scala/org/apache/flink/ml/math/distributed/BlockMapper.scala
---
@@ -0,0 +1,107 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.math.distributed
+
+import
org.apache.flink.ml.math.distributed.DistributedMatrix.{MatrixColIndex,
MatrixRowIndex}
+
+/**
+ * This class is in charge of handling all the spatial logic required by
BlockMatrix.
+ * It introduces a new space of zero-indexed coordinates (i,j), called
"mapped coordinates".
+ * This is a space where blocks are indexed (starting from zero).
+ *
+ * So every coordinate in the original space can be mapped to this space
and to the
+ * corrisponding block. A block have a row and a column coordinate that
explicits
+ * its position. Every set of coordinates in the mapped space corresponds
to a square
+ * of size rowPerBlock x colsPerBlock.
+ *
+ */
+case class BlockMapper( //original matrix size
+ numRows: Int,
+ numCols: Int,
+ //block size
+ rowsPerBlock: Int,
+ colsPerBlock: Int) {
+
+ require(numRows >= rowsPerBlock && numCols >= colsPerBlock)
+ val numBlockRows: Int = math.ceil(numRows * 1.0 / rowsPerBlock).toInt
+ val numBlockCols: Int = math.ceil(numCols * 1.0 / colsPerBlock).toInt
+ val numBlocks = numBlockCols * numBlockRows
+
+ /**
+ * Translates absolute coordinates to the mapped coordinates of the
block
+ * these coordinates belong to.
+ * @param i
+ * @param j
+ * @return
+ */
+ def absCoordToMappedCoord(i: MatrixRowIndex, j: MatrixColIndex): (Int,
Int) =
+ getBlockMappedCoordinates(getBlockIdByCoordinates(i, j))
+
+ /**
+ * Retrieves a block id from original coordinates
+ * @param i Original row
+ * @param j Original column
+ * @return Block ID
+ */
+ def getBlockIdByCoordinates(i: MatrixRowIndex, j: MatrixColIndex): Int =
{
+
+ if (i < 0 || j < 0 || i >= numRows || j >= numCols) {
+ throw new IllegalArgumentException(s"Invalid coordinates ($i,$j).")
+ } else {
+ val mappedRow = i / rowsPerBlock
+ val mappedColumn = j / colsPerBlock
+ val res = mappedRow * numBlockCols + mappedColumn
+
+ assert(res <= numBlocks)
+ res
+ }
+ }
+
+ /**
+ * Retrieves mapped coordinates for a given block.
+ * @param blockId
+ * @return
+ */
+ def getBlockMappedCoordinates(blockId: Int): (Int, Int) = {
+ if (blockId < 0 || blockId > numBlockCols * numBlockRows) {
+ throw new IllegalArgumentException(
+ s"BlockId numeration starts from 0. $blockId is not a valid Id"
+ )
+ } else {
+ val i = blockId / numBlockCols
+ val j = blockId % numBlockCols
+ (i, j)
+ }
+ }
+
+ /**
+ * Retrieves the ID of the block at the given coordinates
+ * @param i
+ * @param j
+ * @return
+ */
+ def getBlockIdByMappedCoord(i: Int, j: Int): Int = {
+
+ if (i < 0 || j < 0 || i >= numBlockRows || j >= numBlockCols) {
+ throw new IllegalArgumentException(s"Invalid coordinates ($i,$j).")
--- End diff --
Please use `require`.
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