[SPARK-15883][MLLIB][DOCS] Fix broken links in mllib documents

## What changes were proposed in this pull request?

This issue fixes all broken links on Spark 2.0 preview MLLib documents. Also, this contains some editorial change.

**Fix broken links**
  * mllib-data-types.md
  * mllib-decision-tree.md
  * mllib-ensembles.md
  * mllib-feature-extraction.md
  * mllib-pmml-model-export.md
  * mllib-statistics.md

**Fix malformed section header and scala coding style**
  * mllib-linear-methods.md

**Replace indirect forward links with direct one**
  * ml-classification-regression.md

## How was this patch tested?

Manual tests (with `cd docs; jekyll build`.)

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #13608 from dongjoon-hyun/SPARK-15883.

docs/ml-classification-regression.md

@@ -815,7 +815,7 @@ The main differences between this API and the [original MLlib ensembles API](mll
 ## Random Forests
 
 [Random forests](http://en.wikipedia.org/wiki/Random_forest)
-are ensembles of [decision trees](ml-decision-tree.html).
+are ensembles of [decision trees](ml-classification-regression.html#decision-trees).
 Random forests combine many decision trees in order to reduce the risk of overfitting.
 The `spark.ml` implementation supports random forests for binary and multiclass classification and for regression,
 using both continuous and categorical features.
@@ -896,7 +896,7 @@ All output columns are optional; to exclude an output column, set its correspond
 ## Gradient-Boosted Trees (GBTs)
 
 [Gradient-Boosted Trees (GBTs)](http://en.wikipedia.org/wiki/Gradient_boosting)
-are ensembles of [decision trees](ml-decision-tree.html).
+are ensembles of [decision trees](ml-classification-regression.html#decision-trees).
 GBTs iteratively train decision trees in order to minimize a loss function.
 The `spark.ml` implementation supports GBTs for binary classification and for regression,
 using both continuous and categorical features.

docs/mllib-data-types.md

@@ -33,7 +33,7 @@ implementations: [`DenseVector`](api/scala/index.html#org.apache.spark.mllib.lin
 using the factory methods implemented in
 [`Vectors`](api/scala/index.html#org.apache.spark.mllib.linalg.Vectors$) to create local vectors.
 
-Refer to the [`Vector` Scala docs](api/scala/index.html#org.apache.spark.mllib.linalg.Vector) and [`Vectors` Scala docs](api/scala/index.html#org.apache.spark.mllib.linalg.Vectors) for details on the API.
+Refer to the [`Vector` Scala docs](api/scala/index.html#org.apache.spark.mllib.linalg.Vector) and [`Vectors` Scala docs](api/scala/index.html#org.apache.spark.mllib.linalg.Vectors$) for details on the API.
 
 {% highlight scala %}
 import org.apache.spark.mllib.linalg.{Vector, Vectors}
@@ -199,7 +199,7 @@ After loading, the feature indices are converted to zero-based.
 [`MLUtils.loadLibSVMFile`](api/scala/index.html#org.apache.spark.mllib.util.MLUtils$) reads training
 examples stored in LIBSVM format.
 
-Refer to the [`MLUtils` Scala docs](api/scala/index.html#org.apache.spark.mllib.util.MLUtils) for details on the API.
+Refer to the [`MLUtils` Scala docs](api/scala/index.html#org.apache.spark.mllib.util.MLUtils$) for details on the API.
 
 {% highlight scala %}
 import org.apache.spark.mllib.regression.LabeledPoint
@@ -264,7 +264,7 @@ We recommend using the factory methods implemented
 in [`Matrices`](api/scala/index.html#org.apache.spark.mllib.linalg.Matrices$) to create local
 matrices. Remember, local matrices in MLlib are stored in column-major order.
 
-Refer to the [`Matrix` Scala docs](api/scala/index.html#org.apache.spark.mllib.linalg.Matrix) and [`Matrices` Scala docs](api/scala/index.html#org.apache.spark.mllib.linalg.Matrices) for details on the API.
+Refer to the [`Matrix` Scala docs](api/scala/index.html#org.apache.spark.mllib.linalg.Matrix) and [`Matrices` Scala docs](api/scala/index.html#org.apache.spark.mllib.linalg.Matrices$) for details on the API.
 
 {% highlight scala %}
 import org.apache.spark.mllib.linalg.{Matrix, Matrices}
@@ -331,7 +331,7 @@ sm = Matrices.sparse(3, 2, [0, 1, 3], [0, 2, 1], [9, 6, 8])
 A distributed matrix has long-typed row and column indices and double-typed values, stored
 distributively in one or more RDDs.  It is very important to choose the right format to store large
 and distributed matrices.  Converting a distributed matrix to a different format may require a
-global shuffle, which is quite expensive.  Three types of distributed matrices have been implemented
+global shuffle, which is quite expensive. Four types of distributed matrices have been implemented
 so far.
 
 The basic type is called `RowMatrix`. A `RowMatrix` is a row-oriented distributed
@@ -344,6 +344,8 @@ An `IndexedRowMatrix` is similar to a `RowMatrix` but with row indices,
 which can be used for identifying rows and executing joins.
 A `CoordinateMatrix` is a distributed matrix stored in [coordinate list (COO)](https://en.wikipedia.org/wiki/Sparse_matrix#Coordinate_list_.28COO.29) format,
 backed by an RDD of its entries.
+A `BlockMatrix` is a distributed matrix backed by an RDD of `MatrixBlock`
+which is a tuple of `(Int, Int, Matrix)`.
 
 ***Note***
 
@@ -535,12 +537,6 @@ rowsRDD = mat.rows
 
 # Convert to a RowMatrix by dropping the row indices.
 rowMat = mat.toRowMatrix()
-
-# Convert to a CoordinateMatrix.
-coordinateMat = mat.toCoordinateMatrix()
-
-# Convert to a BlockMatrix.
-blockMat = mat.toBlockMatrix()
 {% endhighlight %}
 </div>
 

docs/mllib-decision-tree.md

@@ -136,7 +136,7 @@ When tuning these parameters, be careful to validate on held-out test data to av
 
 * **`maxDepth`**: Maximum depth of a tree.  Deeper trees are more expressive (potentially allowing higher accuracy), but they are also more costly to train and are more likely to overfit.
 
-* **`minInstancesPerNode`**: For a node to be split further, each of its children must receive at least this number of training instances.  This is commonly used with [RandomForest](api/scala/index.html#org.apache.spark.mllib.tree.RandomForest) since those are often trained deeper than individual trees.
+* **`minInstancesPerNode`**: For a node to be split further, each of its children must receive at least this number of training instances.  This is commonly used with [RandomForest](api/scala/index.html#org.apache.spark.mllib.tree.RandomForest$) since those are often trained deeper than individual trees.
 
 * **`minInfoGain`**: For a node to be split further, the split must improve at least this much (in terms of information gain).
 
@@ -152,13 +152,13 @@ These parameters may be tuned.  Be careful to validate on held-out test data whe
   * The default value is conservatively chosen to be 256 MB to allow the decision algorithm to work in most scenarios.  Increasing `maxMemoryInMB` can lead to faster training (if the memory is available) by allowing fewer passes over the data.  However, there may be decreasing returns as `maxMemoryInMB` grows since the amount of communication on each iteration can be proportional to `maxMemoryInMB`.
   * *Implementation details*: For faster processing, the decision tree algorithm collects statistics about groups of nodes to split (rather than 1 node at a time).  The number of nodes which can be handled in one group is determined by the memory requirements (which vary per features).  The `maxMemoryInMB` parameter specifies the memory limit in terms of megabytes which each worker can use for these statistics.
 
-* **`subsamplingRate`**: Fraction of the training data used for learning the decision tree.  This parameter is most relevant for training ensembles of trees (using [`RandomForest`](api/scala/index.html#org.apache.spark.mllib.tree.RandomForest) and [`GradientBoostedTrees`](api/scala/index.html#org.apache.spark.mllib.tree.GradientBoostedTrees)), where it can be useful to subsample the original data.  For training a single decision tree, this parameter is less useful since the number of training instances is generally not the main constraint.
+* **`subsamplingRate`**: Fraction of the training data used for learning the decision tree.  This parameter is most relevant for training ensembles of trees (using [`RandomForest`](api/scala/index.html#org.apache.spark.mllib.tree.RandomForest$) and [`GradientBoostedTrees`](api/scala/index.html#org.apache.spark.mllib.tree.GradientBoostedTrees)), where it can be useful to subsample the original data.  For training a single decision tree, this parameter is less useful since the number of training instances is generally not the main constraint.
 
 * **`impurity`**: Impurity measure (discussed above) used to choose between candidate splits.  This measure must match the `algo` parameter.
 
 ### Caching and checkpointing
 
-MLlib 1.2 adds several features for scaling up to larger (deeper) trees and tree ensembles.  When `maxDepth` is set to be large, it can be useful to turn on node ID caching and checkpointing.  These parameters are also useful for [RandomForest](api/scala/index.html#org.apache.spark.mllib.tree.RandomForest) when `numTrees` is set to be large.
+MLlib 1.2 adds several features for scaling up to larger (deeper) trees and tree ensembles.  When `maxDepth` is set to be large, it can be useful to turn on node ID caching and checkpointing.  These parameters are also useful for [RandomForest](api/scala/index.html#org.apache.spark.mllib.tree.RandomForest$) when `numTrees` is set to be large.
 
 * **`useNodeIdCache`**: If this is set to true, the algorithm will avoid passing the current model (tree or trees) to executors on each iteration.
   * This can be useful with deep trees (speeding up computation on workers) and for large Random Forests (reducing communication on each iteration).

docs/mllib-ensembles.md

@@ -9,7 +9,7 @@ displayTitle: Ensembles - spark.mllib
 
 An [ensemble method](http://en.wikipedia.org/wiki/Ensemble_learning)
 is a learning algorithm which creates a model composed of a set of other base models.
-`spark.mllib` supports two major ensemble algorithms: [`GradientBoostedTrees`](api/scala/index.html#org.apache.spark.mllib.tree.GradientBoostedTrees) and [`RandomForest`](api/scala/index.html#org.apache.spark.mllib.tree.RandomForest).
+`spark.mllib` supports two major ensemble algorithms: [`GradientBoostedTrees`](api/scala/index.html#org.apache.spark.mllib.tree.GradientBoostedTrees) and [`RandomForest`](api/scala/index.html#org.apache.spark.mllib.tree.RandomForest$).
 Both use [decision trees](mllib-decision-tree.html) as their base models.
 
 ## Gradient-Boosted Trees vs. Random Forests
@@ -96,7 +96,7 @@ The test error is calculated to measure the algorithm accuracy.
 <div class="codetabs">
 
 <div data-lang="scala" markdown="1">
-Refer to the [`RandomForest` Scala docs](api/scala/index.html#org.apache.spark.mllib.tree.RandomForest) and [`RandomForestModel` Scala docs](api/scala/index.html#org.apache.spark.mllib.tree.model.RandomForestModel) for details on the API.
+Refer to the [`RandomForest` Scala docs](api/scala/index.html#org.apache.spark.mllib.tree.RandomForest$) and [`RandomForestModel` Scala docs](api/scala/index.html#org.apache.spark.mllib.tree.model.RandomForestModel) for details on the API.
 
 {% include_example scala/org/apache/spark/examples/mllib/RandomForestClassificationExample.scala %}
 </div>
@@ -127,7 +127,7 @@ The Mean Squared Error (MSE) is computed at the end to evaluate
 <div class="codetabs">
 
 <div data-lang="scala" markdown="1">
-Refer to the [`RandomForest` Scala docs](api/scala/index.html#org.apache.spark.mllib.tree.RandomForest) and [`RandomForestModel` Scala docs](api/scala/index.html#org.apache.spark.mllib.tree.model.RandomForestModel) for details on the API.
+Refer to the [`RandomForest` Scala docs](api/scala/index.html#org.apache.spark.mllib.tree.RandomForest$) and [`RandomForestModel` Scala docs](api/scala/index.html#org.apache.spark.mllib.tree.model.RandomForestModel) for details on the API.
 
 {% include_example scala/org/apache/spark/examples/mllib/RandomForestRegressionExample.scala %}
 </div>

docs/mllib-feature-extraction.md

@@ -333,7 +333,7 @@ Details you can read at [dimensionality reduction](mllib-dimensionality-reductio
 
 The following code demonstrates how to compute principal components on a `Vector`
 and use them to project the vectors into a low-dimensional space while keeping associated labels
-for calculation a [Linear Regression]((mllib-linear-methods.html))
+for calculation a [Linear Regression](mllib-linear-methods.html)
 
 <div class="codetabs">
 <div data-lang="scala" markdown="1">

docs/mllib-linear-methods.md

@@ -185,10 +185,10 @@ algorithm for 200 iterations.
 import org.apache.spark.mllib.optimization.L1Updater
 
 val svmAlg = new SVMWithSGD()
-svmAlg.optimizer.
-  setNumIterations(200).
-  setRegParam(0.1).
-  setUpdater(new L1Updater)
+svmAlg.optimizer
+  .setNumIterations(200)
+  .setRegParam(0.1)
+  .setUpdater(new L1Updater)
 val modelL1 = svmAlg.run(training)
 {% endhighlight %}
 
@@ -395,7 +395,7 @@ section of the Spark
 quick-start guide. Be sure to also include *spark-mllib* to your build file as
 a dependency.
 
-###Streaming linear regression
+### Streaming linear regression
 
 When data arrive in a streaming fashion, it is useful to fit regression models online,
 updating the parameters of the model as new data arrives. `spark.mllib` currently supports

docs/mllib-pmml-model-export.md

@@ -47,7 +47,7 @@ To export a supported `model` (see table above) to PMML, simply call `model.toPM
 
 As well as exporting the PMML model to a String (`model.toPMML` as in the example above), you can export the PMML model to other formats.
 
-Refer to the [`KMeans` Scala docs](api/scala/index.html#org.apache.spark.mllib.clustering.KMeans) and [`Vectors` Scala docs](api/scala/index.html#org.apache.spark.mllib.linalg.Vectors) for details on the API.
+Refer to the [`KMeans` Scala docs](api/scala/index.html#org.apache.spark.mllib.clustering.KMeans) and [`Vectors` Scala docs](api/scala/index.html#org.apache.spark.mllib.linalg.Vectors$) for details on the API.
 
 Here a complete example of building a KMeansModel and print it out in PMML format:
 {% include_example scala/org/apache/spark/examples/mllib/PMMLModelExportExample.scala %}

docs/mllib-statistics.md

@@ -80,7 +80,7 @@ correlation methods are currently Pearson's and Spearman's correlation.
 calculate correlations between series. Depending on the type of input, two `RDD[Double]`s or
 an `RDD[Vector]`, the output will be a `Double` or the correlation `Matrix` respectively.
 
-Refer to the [`Statistics` Scala docs](api/scala/index.html#org.apache.spark.mllib.stat.Statistics) for details on the API.
+Refer to the [`Statistics` Scala docs](api/scala/index.html#org.apache.spark.mllib.stat.Statistics$) for details on the API.
 
 {% include_example scala/org/apache/spark/examples/mllib/CorrelationsExample.scala %}
 </div>
@@ -210,7 +210,7 @@ message.
 run a 1-sample, 2-sided Kolmogorov-Smirnov test. The following example demonstrates how to run
 and interpret the hypothesis tests.
 
-Refer to the [`Statistics` Scala docs](api/scala/index.html#org.apache.spark.mllib.stat.Statistics) for details on the API.
+Refer to the [`Statistics` Scala docs](api/scala/index.html#org.apache.spark.mllib.stat.Statistics$) for details on the API.
 
 {% include_example scala/org/apache/spark/examples/mllib/HypothesisTestingKolmogorovSmirnovTestExample.scala %}
 </div>
@@ -277,12 +277,12 @@ uniform, standard normal, or Poisson.
 
 <div class="codetabs">
 <div data-lang="scala" markdown="1">
-[`RandomRDDs`](api/scala/index.html#org.apache.spark.mllib.random.RandomRDDs) provides factory
+[`RandomRDDs`](api/scala/index.html#org.apache.spark.mllib.random.RandomRDDs$) provides factory
 methods to generate random double RDDs or vector RDDs.
 The following example generates a random double RDD, whose values follows the standard normal
 distribution `N(0, 1)`, and then map it to `N(1, 4)`.
 
-Refer to the [`RandomRDDs` Scala docs](api/scala/index.html#org.apache.spark.mllib.random.RandomRDDs) for details on the API.
+Refer to the [`RandomRDDs` Scala docs](api/scala/index.html#org.apache.spark.mllib.random.RandomRDDs$) for details on the API.
 
 {% highlight scala %}
 import org.apache.spark.SparkContext