Bagging (Bootstrap Aggregation) Tree Regression is Just a Special Case of Random Forest Regression

Years ago, when I was first exposed to tree-based regression techniques, most of the resources talked about bagging tree regression and random forest regression as if they were two distinct techniques. But in fact, bagging tree regression is just a special case of random forest regression.

I suspect the cause of the confusion is the fact that bagging (“bootstrap aggregation”) tree regression was first described in 1994 paper by a fellow named Leo Breiman. Then seven years later, Breiman slightly modified bagging tree regression and called the new technique random forest regression. So, even though bagging tree regression is just a special case of random forest regression, the term bagging tree regression had been in use for seven years so there was no getting rid of that term.

A simple decision tree for regression will almost always overfit the training data where the model accuracy on the training data is near 100% but accuracy on new, previously unseen data is very poor.

The simple idea of bagging tree regression is to create a collection/ensemble of many simple decision trees, where each tree is trained on a different subset of the rows of the training data. For example, if the source set of training data has 200 rows, you could create 50 simple trees, where each tree is trained on 180 randomly selected rows. The selection is done “with replacement” so for a random subset of training data, some rows will be used more than once and some rows won’t be used at all.

After all the trees are trained, a prediction for an input vector x is just the average of the predictions of the trees in the collection. A very simple and crude idea that sometimes works well, and sometimes doesn’t work very well.

Random forest regression exapnds the idea to include randomly selected columns too, but in a subtle way. Instead of creating subsets of training data that are fixed, random forest regression selects random columns during each split in the split process that constructs the decision trees. For example, if a set of training data has 8 columns of predictors, you might specify to use just 6 randomly selected columns when computing each split.

Because there are many splits computed when a decision tree is built, there is quite a bit of variability introduced into each tree, which acts as a kind of regularization, which discourages model overfitting.

Put another way, bagging tree regression is just random forest regression where all columns are used when computing each split.

The implication is that there’s no need to implement a separate BaggingTreeRegression model — a RandomForestRegression model, with number columns set to the number of columns in the training data has the exact same functionality as bagging tree regression.

Just for fun, I implemented a dedicated BaggingTreeRegession model from scratch, using C#, and a dedicated RandomForestRegression model. I used some synthetic training and test data that has 5 columns of predictor variables. When the random forest model was trained using nCols = 5, the results were the same as the begging tree regression model.

The output of the random forest model:

Begin C# Random Forest regression demo

Loading synthetic train (200) and test (40) data
Done

First three train X:
 -0.1660  0.4406 -0.9998 -0.3953 -0.7065
  0.0776 -0.1616  0.3704 -0.5911  0.7562
 -0.9452  0.3409 -0.1654  0.1174 -0.7192

First three train y:
  0.4840
  0.1568
  0.8054

Setting nTrees = 100
Setting maxDepth = 6
Setting minSamples = 2
Setting minLeaf = 1
Setting nCols = 5
Setting nRows = 150

Creating and training random forest regression model
Done

Accuracy train (within 0.10) = 0.8050
Accuracy test (within 0.10) = 0.5750

MSE train = 0.0006
MSE test = 0.0016

Predicting for x =
  -0.1660   0.4406  -0.9998  -0.3953  -0.7065
y = 0.4728

End demo

The key output statements of the dedicated bagging tree regression program are identical, as expected:

Begin C# Bagging Tree regression demo

Setting nTrees = 100
Setting maxDepth = 6
Setting minSamples = 2
Setting minLeaf = 1
Setting nRows = 150
(Using all columns)

Creating and training BaggingTreeRegression model
Done

Accuracy train (within 0.10) = 0.8050
Accuracy test (within 0.10) = 0.5750

MSE train = 0.0006
MSE test = 0.0016

Predicting for x =
  -0.1660   0.4406  -0.9998  -0.3953  -0.7065
y = 0.4728

Notice that the model still overfits quite a bit. This is because the synthetic data is more or less spead evenly. Because of this weakness, the more powerful gradient boosting regression model is often used instead of bagging tree regression or random forest regression. That said however, for some problem scenarios, bagging tree and random forest regression work quite well.



Machine learning trees are good. Some trees in old science fiction movies are not good.

Left: “Medusa Against the Son of Hercules” (1963) – In this sword-and-sandaler, the medusa is a tree-like plant that turns its victims into stone. My personal grade = C.

Center: “From Hell it Came” (1957) – I saw this dozens of times on TV when I was young. Nuclear radiation + witch doctor + tree = a very bad tree. My personal grade = B-.

Right: “Amazons” (1986) – A group of reptile men kidnap virgins from neighboring villages to sacrifce them to a demonic tree. The tree has a very creepy face, but it’s not clear if he intends to eat the sacrificial virgins or not. My personal grade = C-.


Demo program. Replace “lt” (less than), “gt”, “lte”, “gte” with Boolean operator symbols (my blog editor often chokes on symbols).

using System;
using System.IO;
using System.Collections.Generic;

namespace RandomForestRegression
{
  internal class RandomForestRegressionProgram
  {
    static void Main(string[] args)
    {
      Console.WriteLine("\nBegin C# Random Forest" +
        " regression demo ");

      // 1. load data
      Console.WriteLine("\nLoading synthetic train (200)" +
        " and test (40) data");
      string trainFile =
        "..\\..\\..\\Data\\synthetic_train_200.txt";
      int[] colsX = new int[] { 0, 1, 2, 3, 4 };
      double[][] trainX =
        MatLoad(trainFile, colsX, ',', "#");
      double[] trainY =
        MatToVec(MatLoad(trainFile,
        new int[] { 5 }, ',', "#"));

      string testFile =
        "..\\..\\..\\Data\\synthetic_test_40.txt";
      double[][] testX =
        MatLoad(testFile, colsX, ',', "#");
      double[] testY =
        MatToVec(MatLoad(testFile,
        new int[] { 5 }, ',', "#"));
      Console.WriteLine("Done ");

      Console.WriteLine("\nFirst three train X: ");
      for (int i = 0; i "lt" 3; ++i)
        VecShow(trainX[i], 4, 8);

      Console.WriteLine("\nFirst three train y: ");
      for (int i = 0; i "lt" 3; ++i)
        Console.WriteLine(trainY[i].ToString("F4").
          PadLeft(8));

      // 2. create and train model
      //int nTrees = 150;  // aka n_estimators
      //int maxDepth = 8;
      //int minSamples = 2;
      //int minLeaf = 1;
      //int nCols = 4;  // aka max_features
      //int nRows = 190;  // aka max_samples

      int nTrees = 100;
      int maxDepth = 6;
      int minSamples = 2;
      int minLeaf = 1;
      int nCols = 5;  // use all
      int nRows = 150;  // train data for each tree

      Console.WriteLine("\nSetting nTrees = " + nTrees);
      Console.WriteLine("Setting maxDepth = " + maxDepth);
      Console.WriteLine("Setting minSamples = " + 
        minSamples);
      Console.WriteLine("Setting minLeaf = " + minLeaf);
      Console.WriteLine("Setting nCols = " + nCols);
      Console.WriteLine("Setting nRows = " + nRows);

      Console.WriteLine("\nCreating and training" +
        " random forest regression model ");
      RandomForestRegressor rfr =
        new RandomForestRegressor(nTrees, maxDepth,
        minSamples, minLeaf, nCols, nRows, seed: 0);
      rfr.Train(trainX, trainY);
      Console.WriteLine("Done ");

      // 3. evaluate model
      double accTrain = rfr.Accuracy(trainX, trainY, 0.10);
      Console.WriteLine("\nAccuracy train (within 0.10) = " +
        accTrain.ToString("F4"));
      double accTest = rfr.Accuracy(testX, testY, 0.10);
      Console.WriteLine("Accuracy test (within 0.10) = " +
        accTest.ToString("F4"));

      double mseTrain = rfr.MSE(trainX, trainY);
      Console.WriteLine("\nMSE train = " +
        mseTrain.ToString("F4"));
      double mseTest = rfr.MSE(testX, testY);
      Console.WriteLine("MSE test = " +
        mseTest.ToString("F4"));

      // 4. use model
      double[] x = trainX[0];
      Console.WriteLine("\nPredicting for x = ");
      VecShow(x, 4, 9);
      double predY = rfr.Predict(x);
      Console.WriteLine("y = " + predY.ToString("F4"));

      Console.WriteLine("\nEnd demo ");
      Console.ReadLine();
    } // Main()

    // ------------------------------------------------------
    // helpers for Main()
    // ------------------------------------------------------

    static double[][] MatLoad(string fn, int[] usecols,
      char sep, string comment)
    {
      List"lt"double[]"gt" result =
        new List"lt"double[]"gt"();
      string line = "";
      FileStream ifs = new FileStream(fn, FileMode.Open);
      StreamReader sr = new StreamReader(ifs);
      while ((line = sr.ReadLine()) != null)
      {
        if (line.StartsWith(comment) == true)
          continue;
        string[] tokens = line.Split(sep);
        List"lt"double"gt" lst = new List"lt"double"gt"();
        for (int j = 0; j "lt" usecols.Length; ++j)
          lst.Add(double.Parse(tokens[usecols[j]]));
        double[] row = lst.ToArray();
        result.Add(row);
      }
      sr.Close(); ifs.Close();
      return result.ToArray();
    }

    static double[] MatToVec(double[][] M)
    {
      int nRows = M.Length;
      int nCols = M[0].Length;
      double[] result = new double[nRows * nCols];
      int k = 0;
      for (int i = 0; i "lt" nRows; ++i)
        for (int j = 0; j "lt" nCols; ++j)
          result[k++] = M[i][j];
      return result;
    }

    static void VecShow(double[] vec, int dec, int wid)
    {
      for (int i = 0; i "lt" vec.Length; ++i)
        Console.Write(vec[i].ToString("F" + dec).
          PadLeft(wid));
      Console.WriteLine("");
    }

  } // class Program

  // ========================================================

  public class RandomForestRegressor
  {
    public int nTrees;
    public int maxDepth;
    public int minSamples;
    public int minLeaf;
    public int nSplitCols;  // num cols each split
    public int nRows;
    public List"lt"DecisionTreeRegressor"gt" trees;
    public Random rnd;

    public RandomForestRegressor(int nTrees, int maxDepth,
      int minSamples, int minLeaf, int nCols, int nRows,
      int seed = 0)
    {
      this.nTrees = nTrees;
      this.maxDepth = maxDepth;
      this.minSamples = minSamples;
      this.minLeaf = minLeaf;
      this.nRows = nRows;
      this.nSplitCols = nCols;  // pass to DecisionTree
      this.trees = 
        new List"lt"DecisionTreeRegressor"gt"();
      this.rnd = new Random(seed);
    }

    // ------------------------------------------------------

    public void Train(double[][] trainX, double[] trainY)
    {
      int nr = trainX.Length;
      // int nc = trainX[0].Length;

      for (int i = 0; i "lt" this.nTrees; ++i)
      {
        // construct data rows-subset 
        int[] rndRows =
          GetRandomRowIdxs(nr, this.nRows, this.rnd);
        double[][] subsetX =
          MakeRowsSubsetX(trainX, rndRows);
        double[] subsetY =
          MakeSubsetY(trainY, rndRows);

        // make and train curr tree
        DecisionTreeRegressor dtr =
          new DecisionTreeRegressor(this.maxDepth,
          this.minSamples, this.minLeaf, this.nSplitCols);
        // random cols will be used during splits
        dtr.Train(subsetX, subsetY);
        this.trees.Add(dtr);
      } // i
    }

    // ------------------------------------------------------

    public double Predict(double[] x)
    {
      double sum = 0.0;
      for (int t = 0; t "lt" this.nTrees; ++t)
        sum += this.trees[t].Predict(x);
      return sum / this.nTrees;
    }

    // ------------------------------------------------------

    public double Accuracy(double[][] dataX, double[] dataY,
      double pctClose)
    {
      int numCorrect = 0; int numWrong = 0;
      for (int i = 0; i "lt" dataX.Length; ++i)
      {
        double actualY = dataY[i];
        double predY = this.Predict(dataX[i]);
        if (Math.Abs(predY - actualY) "lt"
          Math.Abs(pctClose * actualY))
          ++numCorrect;
        else
          ++numWrong;
      }
      return (numCorrect * 1.0) / (numWrong + numCorrect);
    }

    // ------------------------------------------------------

    public double MSE(double[][] dataX, double[] dataY)
    {
      int n = dataX.Length;
      double sum = 0.0;
      for (int i = 0; i "lt" n; ++i)
      {
        double actualY = dataY[i];
        double predY = this.Predict(dataX[i]);
        sum += (actualY - predY) * (actualY - predY);
      }
      return sum / n;
    }

    // ------------------------------------------------------

    private static int[] GetRandomRowIdxs(int N, int n,
      Random rnd)
    {
      // pick n rows from N with replacement
      int[] result = new int[n];
      for (int i = 0; i "lt" n; ++i)
        result[i] = rnd.Next(0, N);
      Array.Sort(result);
      return result;
    }

    private static double[][] MakeRowsSubsetX(double[][]
      trainX, int[] rndRows)
    {
      int nCols = trainX[0].Length;  // use all cols
      double[][] result = new double[rndRows.Length][];
      for (int i = 0; i "lt" rndRows.Length; ++i)
        result[i] = new double[nCols];

      for (int i = 0; i "lt" rndRows.Length; ++i)
      {
        for (int j = 0; j "lt" nCols; ++j)
        {
          int r = rndRows[i]; // random row in trainX
          result[i][j] = trainX[r][j];
        }
      }
      return result;
    }

    private static double[] MakeSubsetY(double[] trainY,
      int[] rndRows)
    {
      double[] result = new double[rndRows.Length];
      for (int i = 0; i "lt" rndRows.Length; ++i)
        result[i] = trainY[rndRows[i]];
      return result;
    }

  } // class RandomForestRegression

  // ========================================================

  // simplified list-based tree

  // ========================================================

  public class DecisionTreeRegressor
  {
    public int maxDepth;
    public int minSamples;  // aka min_samples_split
    public int minLeaf;  // min number of values in a leaf
    public int numSplitCols; // mostly for random forest
    public List"lt"Node"gt" tree = new List"lt"Node"gt"();
    public Random rnd;  // order in which cols are searched

    public double[][] trainX;  // store data by ref
    public double[] trainY;

    // ------------------------------------------------------

    public class Node
    {
      public int id;
      public int colIdx;  // aka featureIdx
      public double thresh;
      public int left;  // index into List
      public int right;
      public double value;
      public bool isLeaf;
      public List"lt"int"gt" rows;  // assoc rows in train data

      public Node()
      {
        this.id = -1;
        this.colIdx = -1;
        this.thresh = 0.0;  // aka split value
        this.left = -1;
        this.right = -1;
        this.value = 0.0;  // aka pred y
        this.isLeaf = false;
        this.rows = null;
      }
    } // class Node

    // --------------------------------------------

    public DecisionTreeRegressor(int maxDepth = 2,
      int minSamples = 2, int minLeaf = 1,
      int numSplitCols = -1, int seed = 0)
    {
      // if maxDepth = 0, tree has just a root node
      // if maxDepth = 1, at most 3 nodes (root, l, r)
      // if maxDepth = n, at most 2^(n+1) - 1 nodes
      this.maxDepth = maxDepth;
      this.minSamples = minSamples;
      this.minLeaf = minLeaf;
      this.numSplitCols = numSplitCols;  // for ran. forest

      // create full tree List with null nodes
      int numNodes = (int)Math.Pow(2, (maxDepth + 1)) - 1;
      for (int i = 0; i "lt" numNodes; ++i)
      {
        this.tree.Add(null);  // empty nodes
      }
      this.rnd = new Random(seed);
    }

    // ------------------------------------------------------
    // public: Train(), Predict(), Explain(), Accuracy(),
    //   MSE(), Display().
    // helpers: MakeTree(), BestSplit(), TreeTargetMean(),
    //   TreeTargetVariance().
    // ------------------------------------------------------

    public void Train(double[][] trainX, double[] trainY)
    {
      this.trainX = trainX; // 
      this.trainY = trainY;
      this.MakeTree();
    }

    // ------------------------------------------------------

    public double Predict(double[] x)
    {
      int p = 0;
      Node currNode = this.tree[p];
      while (currNode != null &&
        currNode.isLeaf == false &&
        p "lt" this.tree.Count)
      {
        if (x[currNode.colIdx] "lte" currNode.thresh)
          p = currNode.left;
        else
          p = currNode.right;
        currNode = this.tree[p];
      }
      return this.tree[p].value;
    }

    private void MakeTree()
    {
      // no recursion, no pointers, List storage, no stack
      if (this.numSplitCols == -1) // use all cols
        this.numSplitCols = this.trainX[0].Length;

      // prepare root node
      List"lt"int"gt" allRows = new List"lt"int"gt"();
      for (int i = 0; i "lt" this.trainX.Length; ++i)
        allRows.Add(i);
      double grandMean = this.TreeTargetMean(allRows);

      // wait to supply colIdx and thresh in loop
      Node root = new Node();
      root.id = 0;
      root.left = 1;
      root.right = 2;
      root.value = grandMean;
      root.isLeaf = false; // already set
      root.rows = allRows;
      this.tree[0] = root;

      for (int i = 0; i "lt" this.tree.Count; ++i)
      {
        Node currNode = this.tree[i];
        // curr node has values for everything
        // except colIdx and thresh

        // curr node too deep to have children OR
        // curr node not enough rows to split then
        // leave both children as null
        if (currNode == null ||
          currNode.rows.Count == 0) { continue; }

        // if parent cannot be split, make parent a leaf
        if (currNode.id "gte" (int)Math.Pow(2,
          (this.maxDepth)) - 1 ||
          currNode.rows.Count "lt" this.minSamples)
        {
          currNode.isLeaf = true;
          continue;
        }

        // parent has enough rows to try to split
        double[] splitInfo = this.BestSplit(currNode.rows);
        int colIdx = (int)splitInfo[0];
        double splitVal = splitInfo[1]; //split value

        if (colIdx == -1)  // unable split, is a leaf
        {
          currNode.isLeaf = true;
          continue;
        }

        // complete the fields for curr node
        currNode.colIdx = colIdx;
        currNode.thresh = splitVal;

        // construct the children, 
        // except for colIdx and thresh
        // which will be supplied in amin loop
        Node leftNode = new Node();
        Node rightNode = new Node();

        // construct children rows using split info
        // all info except colIdx and thresh
        List"lt"int"gt" leftIdxs = new List"lt"int"gt"();
        List"lt"int"gt" rightIdxs = new List"lt"int"gt"();
        for (int k = 0; k "lt" currNode.rows.Count; ++k)
        {
          int r = currNode.rows[k];
          if (this.trainX[r][colIdx] "lte" splitVal)
            leftIdxs.Add(r);
          else
            rightIdxs.Add(r);
        }

        leftNode.id = currNode.id * 2 + 1;
        if (leftNode.id "gt" (int)Math.Pow(2,
          (maxDepth + 1)) - 2) leftNode.id = -1;
        leftNode.left = leftNode.id * 2 + 1;
        if (leftNode.left "gt" (int)Math.Pow(2,
          (maxDepth + 1)) - 2) leftNode.left = -1;
        leftNode.right = leftNode.id * 2 + 2;
        if (leftNode.right "gt" (int)Math.Pow(2,
          (maxDepth + 1)) - 2) leftNode.right = -1;

        leftNode.rows = leftIdxs;
        leftNode.value =
          this.TreeTargetMean(leftNode.rows);
        this.tree[leftNode.id] = leftNode;

        rightNode.id = currNode.id * 2 + 2;
        if (rightNode.id "gt" (int)Math.Pow(2,
          (maxDepth + 1)) - 2) rightNode.id = -1;
        rightNode.left = rightNode.id * 2 + 1;
        if (rightNode.left "gt" (int)Math.Pow(2,
          (maxDepth + 1)) - 2) rightNode.left = -1;
        rightNode.right = rightNode.id * 2 + 2;
        if (rightNode.right "gt" (int)Math.Pow(2,
          (maxDepth + 1)) - 2) rightNode.right = -1;
        rightNode.rows = rightIdxs;
        rightNode.value =
          this.TreeTargetMean(rightNode.rows);
        this.tree[rightNode.id] = rightNode;

      } // i
      return;
    }

    // ------------------------------------------------------

    private double[] BestSplit(List"lt"int"gt" rows)
    {
      // implicit params numSplitCols, minLeaf, numsplitCols
      // result[0] = best col idx (as double)
      // result[1] = best split value
      rows.Sort();

      int bestColIdx = -1;  // indicates bad split
      double bestThresh = 0.0;
      double bestVar = double.MaxValue;  // smaller better

      int nRows = rows.Count;  // or dataY.Length
      int nCols = this.trainX[0].Length;

      if (nRows == 0)
      {
        throw new Exception("empty data in BestSplit()");
      }

      // process cols in scrambled order
      int[] colIndices = new int[nCols];
      for (int k = 0; k "lt" nCols; ++k)
        colIndices[k] = k;
      // shuffle, inline Fisher-Yates
      int n = colIndices.Length;
      for (int i = 0; i "lt" n; ++i)
      {
        int ri = rnd.Next(i, n);  // be careful
        int tmp = colIndices[i];
        colIndices[i] = colIndices[ri];
        colIndices[ri] = tmp;
      }

      // numSplitCols is usually all columns (-1)
      for (int j = 0; j "lt" this.numSplitCols; ++j)
      {
        int colIdx = colIndices[j];
        HashSet"lt"double"gt" examineds =
          new HashSet"lt"double"gt"();

        for (int i = 0; i "lt" nRows; ++i) // each row
        {
          // if curr thresh been seen, skip it
          double thresh = this.trainX[rows[i]][colIdx];
          if (examineds.Contains(thresh)) continue;
          examineds.Add(thresh);

          // get row idxs where x is lte, gt thresh
          List"lt"int"gt" leftIdxs = new List"lt"int"gt"();
          List"lt"int"gt" rightIdxs = new List"lt"int"gt"();
          for (int k = 0; k "lt" nRows; ++k)
          {
            if (this.trainX[rows[k]][colIdx] "lte" thresh)
              leftIdxs.Add(rows[k]);
            else
              rightIdxs.Add(rows[k]);
          }

          // Check if proposed split has too few values
          if (leftIdxs.Count "lt" this.minLeaf ||
            rightIdxs.Count "lt" this.minLeaf)
            continue;  // to next row

          double leftVar =
            this.TreeTargetVariance(leftIdxs);
          double rightVar =
            this.TreeTargetVariance(rightIdxs);
          double weightedVar = (leftIdxs.Count * leftVar +
            rightIdxs.Count * rightVar) / nRows;

          if (weightedVar "lt" bestVar)
          {
            // if this never happens, bestColIdx remains -1
            // which means a bad split. used in MakeTree()
            bestColIdx = colIdx;
            bestThresh = thresh;
            bestVar = weightedVar;
          }

        } // each row
      } // j each col

      double[] result = new double[2];  // out params ugly
      result[0] = 1.0 * bestColIdx;
      result[1] = bestThresh;
      return result;

    } // BestSplit()

    // ------------------------------------------------------

    private double TreeTargetMean(List"lt"int"gt" rows)
    {
      // mean of rows items in trainY: for node prediction
      double sum = 0.0;
      for (int i = 0; i "lt" rows.Count; ++i)
      {
        int r = rows[i];
        sum += this.trainY[r];
      }
      return sum / rows.Count;
    }

    // ------------------------------------------------------

    private double TreeTargetVariance(List"lt"int"gt" rows)
    {
      double mean = this.TreeTargetMean(rows);
      double sum = 0.0;
      for (int i = 0; i "lt" rows.Count; ++i)
      {
        int r = rows[i];
        sum += (this.trainY[r] - mean) *
          (this.trainY[r] - mean);
      }
      return sum / rows.Count;
    }

    // ------------------------------------------------------

  } // class DecisionTreeRegressor
} // ns

Training data:

# synthetic_train_200.txt
#
-0.1660,  0.4406, -0.9998, -0.3953, -0.7065,  0.4840
 0.0776, -0.1616,  0.3704, -0.5911,  0.7562,  0.1568
-0.9452,  0.3409, -0.1654,  0.1174, -0.7192,  0.8054
 0.9365, -0.3732,  0.3846,  0.7528,  0.7892,  0.1345
-0.8299, -0.9219, -0.6603,  0.7563, -0.8033,  0.7955
 0.0663,  0.3838, -0.3690,  0.3730,  0.6693,  0.3206
-0.9634,  0.5003,  0.9777,  0.4963, -0.4391,  0.7377
-0.1042,  0.8172, -0.4128, -0.4244, -0.7399,  0.4801
-0.9613,  0.3577, -0.5767, -0.4689, -0.0169,  0.6861
-0.7065,  0.1786,  0.3995, -0.7953, -0.1719,  0.5569
 0.3888, -0.1716, -0.9001,  0.0718,  0.3276,  0.2500
 0.1731,  0.8068, -0.7251, -0.7214,  0.6148,  0.3297
-0.2046, -0.6693,  0.8550, -0.3045,  0.5016,  0.2129
 0.2473,  0.5019, -0.3022, -0.4601,  0.7918,  0.2613
-0.1438,  0.9297,  0.3269,  0.2434, -0.7705,  0.5171
 0.1568, -0.1837, -0.5259,  0.8068,  0.1474,  0.3307
-0.9943,  0.2343, -0.3467,  0.0541,  0.7719,  0.5581
 0.2467, -0.9684,  0.8589,  0.3818,  0.9946,  0.1092
-0.6553, -0.7257,  0.8652,  0.3936, -0.8680,  0.7018
 0.8460,  0.4230, -0.7515, -0.9602, -0.9476,  0.1996
-0.9434, -0.5076,  0.7201,  0.0777,  0.1056,  0.5664
 0.9392,  0.1221, -0.9627,  0.6013, -0.5341,  0.1533
 0.6142, -0.2243,  0.7271,  0.4942,  0.1125,  0.1661
 0.4260,  0.1194, -0.9749, -0.8561,  0.9346,  0.2230
 0.1362, -0.5934, -0.4953,  0.4877, -0.6091,  0.3810
 0.6937, -0.5203, -0.0125,  0.2399,  0.6580,  0.1460
-0.6864, -0.9628, -0.8600, -0.0273,  0.2127,  0.5387
 0.9772,  0.1595, -0.2397,  0.1019,  0.4907,  0.1611
 0.3385, -0.4702, -0.8673, -0.2598,  0.2594,  0.2270
-0.8669, -0.4794,  0.6095, -0.6131,  0.2789,  0.4700
 0.0493,  0.8496, -0.4734, -0.8681,  0.4701,  0.3516
 0.8639, -0.9721, -0.5313,  0.2336,  0.8980,  0.1412
 0.9004,  0.1133,  0.8312,  0.2831, -0.2200,  0.1782
 0.0991,  0.8524,  0.8375, -0.2102,  0.9265,  0.2150
-0.6521, -0.7473, -0.7298,  0.0113, -0.9570,  0.7422
 0.6190, -0.3105,  0.8802,  0.1640,  0.7577,  0.1056
 0.6895,  0.8108, -0.0802,  0.0927,  0.5972,  0.2214
 0.1982, -0.9689,  0.1870, -0.1326,  0.6147,  0.1310
-0.3695,  0.7858,  0.1557, -0.6320,  0.5759,  0.3773
-0.1596,  0.3581,  0.8372, -0.9992,  0.9535,  0.2071
-0.2468,  0.9476,  0.2094,  0.6577,  0.1494,  0.4132
 0.1737,  0.5000,  0.7166,  0.5102,  0.3961,  0.2611
 0.7290, -0.3546,  0.3416, -0.0983, -0.2358,  0.1332
-0.3652,  0.2438, -0.1395,  0.9476,  0.3556,  0.4170
-0.6029, -0.1466, -0.3133,  0.5953,  0.7600,  0.4334
-0.4596, -0.4953,  0.7098,  0.0554,  0.6043,  0.2775
 0.1450,  0.4663,  0.0380,  0.5418,  0.1377,  0.2931
-0.8636, -0.2442, -0.8407,  0.9656, -0.6368,  0.7429
 0.6237,  0.7499,  0.3768,  0.1390, -0.6781,  0.2185
-0.5499,  0.1850, -0.3755,  0.8326,  0.8193,  0.4399
-0.4858, -0.7782, -0.6141, -0.0008,  0.4572,  0.4197
 0.7033, -0.1683,  0.2334, -0.5327, -0.7961,  0.1776
 0.0317, -0.0457, -0.6947,  0.2436,  0.0880,  0.3345
 0.5031, -0.5559,  0.0387,  0.5706, -0.9553,  0.3107
-0.3513,  0.7458,  0.6894,  0.0769,  0.7332,  0.3170
 0.2205,  0.5992, -0.9309,  0.5405,  0.4635,  0.3532
-0.4806, -0.4859,  0.2646, -0.3094,  0.5932,  0.3202
 0.9809, -0.3995, -0.7140,  0.8026,  0.0831,  0.1600
 0.9495,  0.2732,  0.9878,  0.0921,  0.0529,  0.1289
-0.9476, -0.6792,  0.4913, -0.9392, -0.2669,  0.5966
 0.7247,  0.3854,  0.3819, -0.6227, -0.1162,  0.1550
-0.5922, -0.5045, -0.4757,  0.5003, -0.0860,  0.5863
-0.8861,  0.0170, -0.5761,  0.5972, -0.4053,  0.7301
 0.6877, -0.2380,  0.4997,  0.0223,  0.0819,  0.1404
 0.9189,  0.6079, -0.9354,  0.4188, -0.0700,  0.1907
-0.1428, -0.7820,  0.2676,  0.6059,  0.3936,  0.2790
 0.5324, -0.3151,  0.6917, -0.1425,  0.6480,  0.1071
-0.8432, -0.9633, -0.8666, -0.0828, -0.7733,  0.7784
-0.9444,  0.5097, -0.2103,  0.4939, -0.0952,  0.6787
-0.0520,  0.6063, -0.1952,  0.8094, -0.9259,  0.4836
 0.5477, -0.7487,  0.2370, -0.9793,  0.0773,  0.1241
 0.2450,  0.8116,  0.9799,  0.4222,  0.4636,  0.2355
 0.8186, -0.1983, -0.5003, -0.6531, -0.7611,  0.1511
-0.4714,  0.6382, -0.3788,  0.9648, -0.4667,  0.5950
 0.0673, -0.3711,  0.8215, -0.2669, -0.1328,  0.2677
-0.9381,  0.4338,  0.7820, -0.9454,  0.0441,  0.5518
-0.3480,  0.7190,  0.1170,  0.3805, -0.0943,  0.4724
-0.9813,  0.1535, -0.3771,  0.0345,  0.8328,  0.5438
-0.1471, -0.5052, -0.2574,  0.8637,  0.8737,  0.3042
-0.5454, -0.3712, -0.6505,  0.2142, -0.1728,  0.5783
 0.6327, -0.6297,  0.4038, -0.5193,  0.1484,  0.1153
-0.5424,  0.3282, -0.0055,  0.0380, -0.6506,  0.6613
 0.1414,  0.9935,  0.6337,  0.1887,  0.9520,  0.2540
-0.9351, -0.8128, -0.8693, -0.0965, -0.2491,  0.7353
 0.9507, -0.6640,  0.9456,  0.5349,  0.6485,  0.1059
-0.0462, -0.9737, -0.2940, -0.0159,  0.4602,  0.2606
-0.0627, -0.0852, -0.7247, -0.9782,  0.5166,  0.2977
 0.0478,  0.5098, -0.0723, -0.7504, -0.3750,  0.3335
 0.0090,  0.3477,  0.5403, -0.7393, -0.9542,  0.4415
-0.9748,  0.3449,  0.3736, -0.1015,  0.8296,  0.4358
 0.2887, -0.9895, -0.0311,  0.7186,  0.6608,  0.2057
 0.1570, -0.4518,  0.1211,  0.3435, -0.2951,  0.3244
 0.7117, -0.6099,  0.4946, -0.4208,  0.5476,  0.1096
-0.2929, -0.5726,  0.5346, -0.3827,  0.4665,  0.2465
 0.4889, -0.5572, -0.5718, -0.6021, -0.7150,  0.2163
-0.7782,  0.3491,  0.5996, -0.8389, -0.5366,  0.6516
-0.5847,  0.8347,  0.4226,  0.1078, -0.3910,  0.6134
 0.8469,  0.4121, -0.0439, -0.7476,  0.9521,  0.1571
-0.6803, -0.5948, -0.1376, -0.1916, -0.7065,  0.7156
 0.2878,  0.5086, -0.5785,  0.2019,  0.4979,  0.2980
 0.2764,  0.1943, -0.4090,  0.4632,  0.8906,  0.2960
-0.8877,  0.6705, -0.6155, -0.2098, -0.3998,  0.7107
-0.8398,  0.8093, -0.2597,  0.0614, -0.0118,  0.6502
-0.8476,  0.0158, -0.4769, -0.2859, -0.7839,  0.7715
 0.5751, -0.7868,  0.9714, -0.6457,  0.1448,  0.1175
 0.4802, -0.7001,  0.1022, -0.5668,  0.5184,  0.1090
 0.4458, -0.6469,  0.7239, -0.9604,  0.7205,  0.0779
 0.5175,  0.4339,  0.9747, -0.4438, -0.9924,  0.2879
 0.8678,  0.7158,  0.4577,  0.0334,  0.4139,  0.1678
 0.5406,  0.5012,  0.2264, -0.1963,  0.3946,  0.2088
-0.9938,  0.5498,  0.7928, -0.5214, -0.7585,  0.7687
 0.7661,  0.0863, -0.4266, -0.7233, -0.4197,  0.1466
 0.2277, -0.3517, -0.0853, -0.1118,  0.6563,  0.1767
 0.3499, -0.5570, -0.0655, -0.3705,  0.2537,  0.1632
 0.7547, -0.1046,  0.5689, -0.0861,  0.3125,  0.1257
 0.8186,  0.2110,  0.5335,  0.0094, -0.0039,  0.1391
 0.6858, -0.8644,  0.1465,  0.8855,  0.0357,  0.1845
-0.4967,  0.4015,  0.0805,  0.8977,  0.2487,  0.4663
 0.6760, -0.9841,  0.9787, -0.8446, -0.3557,  0.1509
-0.1203, -0.4885,  0.6054, -0.0443, -0.7313,  0.4854
 0.8557,  0.7919, -0.0169,  0.7134, -0.1628,  0.2002
 0.0115, -0.6209,  0.9300, -0.4116, -0.7931,  0.4052
-0.7114, -0.9718,  0.4319,  0.1290,  0.5892,  0.3661
 0.3915,  0.5557, -0.1870,  0.2955, -0.6404,  0.2954
-0.3564, -0.6548, -0.1827, -0.5172, -0.1862,  0.4622
 0.2392, -0.4959,  0.5857, -0.1341, -0.2850,  0.2470
-0.3394,  0.3947, -0.4627,  0.6166, -0.4094,  0.5325
 0.7107,  0.7768, -0.6312,  0.1707,  0.7964,  0.2757
-0.1078,  0.8437, -0.4420,  0.2177,  0.3649,  0.4028
-0.3139,  0.5595, -0.6505, -0.3161, -0.7108,  0.5546
 0.4335,  0.3986,  0.3770, -0.4932,  0.3847,  0.1810
-0.2562, -0.2894, -0.8847,  0.2633,  0.4146,  0.4036
 0.2272,  0.2966, -0.6601, -0.7011,  0.0284,  0.2778
-0.0743, -0.1421, -0.0054, -0.6770, -0.3151,  0.3597
-0.4762,  0.6891,  0.6007, -0.1467,  0.2140,  0.4266
-0.4061,  0.7193,  0.3432,  0.2669, -0.7505,  0.6147
-0.0588,  0.9731,  0.8966,  0.2902, -0.6966,  0.4955
-0.0627, -0.1439,  0.1985,  0.6999,  0.5022,  0.3077
 0.1587,  0.8494, -0.8705,  0.9827, -0.8940,  0.4263
-0.7850,  0.2473, -0.9040, -0.4308, -0.8779,  0.7199
 0.4070,  0.3369, -0.2428, -0.6236,  0.4940,  0.2215
-0.0242,  0.0513, -0.9430,  0.2885, -0.2987,  0.3947
-0.5416, -0.1322, -0.2351, -0.0604,  0.9590,  0.3683
 0.1055,  0.7783, -0.2901, -0.5090,  0.8220,  0.2984
-0.9129,  0.9015,  0.1128, -0.2473,  0.9901,  0.4776
-0.9378,  0.1424, -0.6391,  0.2619,  0.9618,  0.5368
 0.7498, -0.0963,  0.4169,  0.5549, -0.0103,  0.1614
-0.2612, -0.7156,  0.4538, -0.0460, -0.1022,  0.3717
 0.7720,  0.0552, -0.1818, -0.4622, -0.8560,  0.1685
-0.4177,  0.0070,  0.9319, -0.7812,  0.3461,  0.3052
-0.0001,  0.5542, -0.7128, -0.8336, -0.2016,  0.3803
 0.5356, -0.4194, -0.5662, -0.9666, -0.2027,  0.1776
-0.2378,  0.3187, -0.8582, -0.6948, -0.9668,  0.5474
-0.1947, -0.3579,  0.1158,  0.9869,  0.6690,  0.2992
 0.3992,  0.8365, -0.9205, -0.8593, -0.0520,  0.3154
-0.0209,  0.0793,  0.7905, -0.1067,  0.7541,  0.1864
-0.4928, -0.4524, -0.3433,  0.0951, -0.5597,  0.6261
-0.8118,  0.7404, -0.5263, -0.2280,  0.1431,  0.6349
 0.0516, -0.8480,  0.7483,  0.9023,  0.6250,  0.1959
-0.3212,  0.1093,  0.9488, -0.3766,  0.3376,  0.2735
-0.3481,  0.5490, -0.3484,  0.7797,  0.5034,  0.4379
-0.5785, -0.9170, -0.3563, -0.9258,  0.3877,  0.4121
 0.3407, -0.1391,  0.5356,  0.0720, -0.9203,  0.3458
-0.3287, -0.8954,  0.2102,  0.0241,  0.2349,  0.3247
-0.1353,  0.6954, -0.0919, -0.9692,  0.7461,  0.3338
 0.9036, -0.8982, -0.5299, -0.8733, -0.1567,  0.1187
 0.7277, -0.8368, -0.0538, -0.7489,  0.5458,  0.0830
 0.9049,  0.8878,  0.2279,  0.9470, -0.3103,  0.2194
 0.7957, -0.1308, -0.5284,  0.8817,  0.3684,  0.2172
 0.4647, -0.4931,  0.2010,  0.6292, -0.8918,  0.3371
-0.7390,  0.6849,  0.2367,  0.0626, -0.5034,  0.7039
-0.1567, -0.8711,  0.7940, -0.5932,  0.6525,  0.1710
 0.7635, -0.0265,  0.1969,  0.0545,  0.2496,  0.1445
 0.7675,  0.1354, -0.7698, -0.5460,  0.1920,  0.1728
-0.5211, -0.7372, -0.6763,  0.6897,  0.2044,  0.5217
 0.1913,  0.1980,  0.2314, -0.8816,  0.5006,  0.1998
 0.8964,  0.0694, -0.6149,  0.5059, -0.9854,  0.1825
 0.1767,  0.7104,  0.2093,  0.6452,  0.7590,  0.2832
-0.3580, -0.7541,  0.4426, -0.1193, -0.7465,  0.5657
-0.5996,  0.5766, -0.9758, -0.3933, -0.9572,  0.6800
 0.9950,  0.1641, -0.4132,  0.8579,  0.0142,  0.2003
-0.4717, -0.3894, -0.2567, -0.5111,  0.1691,  0.4266
 0.3917, -0.8561,  0.9422,  0.5061,  0.6123,  0.1212
-0.0366, -0.1087,  0.3449, -0.1025,  0.4086,  0.2475
 0.3633,  0.3943,  0.2372, -0.6980,  0.5216,  0.1925
-0.5325, -0.6466, -0.2178, -0.3589,  0.6310,  0.3568
 0.2271,  0.5200, -0.1447, -0.8011, -0.7699,  0.3128
 0.6415,  0.1993,  0.3777, -0.0178, -0.8237,  0.2181
-0.5298, -0.0768, -0.6028, -0.9490,  0.4588,  0.4356
 0.6870, -0.1431,  0.7294,  0.3141,  0.1621,  0.1632
-0.5985,  0.0591,  0.7889, -0.3900,  0.7419,  0.2945
 0.3661,  0.7984, -0.8486,  0.7572, -0.6183,  0.3449
 0.6995,  0.3342, -0.3113, -0.6972,  0.2707,  0.1712
 0.2565,  0.9126,  0.1798, -0.6043, -0.1413,  0.2893
-0.3265,  0.9839, -0.2395,  0.9854,  0.0376,  0.4770
 0.2690, -0.1722,  0.9818,  0.8599, -0.7015,  0.3954
-0.2102, -0.0768,  0.1219,  0.5607, -0.0256,  0.3949
 0.8216, -0.9555,  0.6422, -0.6231,  0.3715,  0.0801
-0.2896,  0.9484, -0.7545, -0.6249,  0.7789,  0.4370
-0.9985, -0.5448, -0.7092, -0.5931,  0.7926,  0.5402

Test data:

# synthetic_test_40.txt
#
 0.7462,  0.4006, -0.0590,  0.6543, -0.0083,  0.1935
 0.8495, -0.2260, -0.0142, -0.4911,  0.7699,  0.1078
-0.2335, -0.4049,  0.4352, -0.6183, -0.7636,  0.5088
 0.1810, -0.5142,  0.2465,  0.2767, -0.3449,  0.3136
-0.8650,  0.7611, -0.0801,  0.5277, -0.4922,  0.7140
-0.2358, -0.7466, -0.5115, -0.8413, -0.3943,  0.4533
 0.4834,  0.2300,  0.3448, -0.9832,  0.3568,  0.1360
-0.6502, -0.6300,  0.6885,  0.9652,  0.8275,  0.3046
-0.3053,  0.5604,  0.0929,  0.6329, -0.0325,  0.4756
-0.7995,  0.0740, -0.2680,  0.2086,  0.9176,  0.4565
-0.2144, -0.2141,  0.5813,  0.2902, -0.2122,  0.4119
-0.7278, -0.0987, -0.3312, -0.5641,  0.8515,  0.4438
 0.3793,  0.1976,  0.4933,  0.0839,  0.4011,  0.1905
-0.8568,  0.9573, -0.5272,  0.3212, -0.8207,  0.7415
-0.5785,  0.0056, -0.7901, -0.2223,  0.0760,  0.5551
 0.0735, -0.2188,  0.3925,  0.3570,  0.3746,  0.2191
 0.1230, -0.2838,  0.2262,  0.8715,  0.1938,  0.2878
 0.4792, -0.9248,  0.5295,  0.0366, -0.9894,  0.3149
-0.4456,  0.0697,  0.5359, -0.8938,  0.0981,  0.3879
 0.8629, -0.8505, -0.4464,  0.8385,  0.5300,  0.1769
 0.1995,  0.6659,  0.7921,  0.9454,  0.9970,  0.2330
-0.0249, -0.3066, -0.2927, -0.4923,  0.8220,  0.2437
 0.4513, -0.9481, -0.0770, -0.4374, -0.9421,  0.2879
-0.3405,  0.5931, -0.3507, -0.3842,  0.8562,  0.3987
 0.9538,  0.0471,  0.9039,  0.7760,  0.0361,  0.1706
-0.0887,  0.2104,  0.9808,  0.5478, -0.3314,  0.4128
-0.8220, -0.6302,  0.0537, -0.1658,  0.6013,  0.4306
-0.4123, -0.2880,  0.9074, -0.0461, -0.4435,  0.5144
 0.0060,  0.2867, -0.7775,  0.5161,  0.7039,  0.3599
-0.7968, -0.5484,  0.9426, -0.4308,  0.8148,  0.2979
 0.7811,  0.8450, -0.6877,  0.7594,  0.2640,  0.2362
-0.6802, -0.1113, -0.8325, -0.6694, -0.6056,  0.6544
 0.3821,  0.1476,  0.7466, -0.5107,  0.2592,  0.1648
 0.7265,  0.9683, -0.9803, -0.4943, -0.5523,  0.2454
-0.9049, -0.9797, -0.0196, -0.9090, -0.4433,  0.6447
-0.4607,  0.1811, -0.2389,  0.4050, -0.0078,  0.5229
 0.2664, -0.2932, -0.4259, -0.7336,  0.8742,  0.1834
-0.4507,  0.1029, -0.6294, -0.1158, -0.6294,  0.6081
 0.8948, -0.0124,  0.9278,  0.2899, -0.0314,  0.1534
-0.1323, -0.8813, -0.0146, -0.0697,  0.6135,  0.2386
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