Gradient Boosting Regression from Scratch Using C# with List-Storage, No-Pointers, No-Recursion, MSE-Split Decision Trees

It’s not easy to explain the topic of this blog post. Bear with me.

The goal of a machine learning regression problem is to predict a single numeric value. For example, predicting the bank account balance of a person based on his annual income, age, years of education, and so on.

There are about a dozen common regression techniques. One of the most powerful, but most complicated, techniques is gradient boosting regression. Gradient boosting regression uses a collection of decision trees that are constructed sequentially. There are many ways to implement a decision tree: list storage vs. pointer storage, recursive construction vs. stack-based construction, maximizing variance reduction splits vs. minimizing quasi-MSE splits, and more.

One morning before work, I put together a demo of gradient boosting regression where the decision trees are implemented using list storage (no pointers), stack-based construction (no recursion), MSE splits.

For my demo, I used one of my standard synthetic datasets. It looks like:

-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
. . . 

The first five values on each line are predictors. The last value is the target y to predict. The data was generated by a 5-10-1 neural network with random weights and biases, so the data has an underlying but very complex structure. There are 200 training items and 40 test items.

The output of my demo is:

Begin C# Gradient Boosting regression demo
Using list tree

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 numTrees = 100
Setting maxDepth = 3
Setting minSamples = 2
Setting minLeaf = 1
Setting lrnRate = 0.1000

Creating and training GradientBoostRegression model
Done

Evaluating model

Accuracy train (within 0.10) = 0.9750
Accuracy test (within 0.10) = 0.8000

MSE train = 0.0001
MSE test = 0.0010

R2 train = 0.9982
R2 test = 0.9629

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

Initial prediction: 0.3493
t =   0  pred_res = -0.0608  delta =  0.0061  pred =  0.3554
t =   1  pred_res = -0.0840  delta =  0.0084  pred =  0.3638
t =   2  pred_res = -0.0704  delta =  0.0070  pred =  0.3708
t =   3  pred_res = -0.1074  delta =  0.0107  pred =  0.3816
t =   4  pred_res = -0.0243  delta =  0.0024  pred =  0.3840
. . .
t =  98  pred_res = -0.0053  delta =  0.0005  pred =  0.4843
t =  99  pred_res =  0.0001  delta = -0.0000  pred =  0.4843
Predicted y = 0.4843

End demo

In my opinion, tuning the parameters of a gradient boosting regression model is more difficult than the tuning for any other type of regression. Changing either of the two GBR parameters (number of trees, learning rate) or any of the three tree parameters (max depth, min samples, min leaf) has a big effect on the GBR prediction model.

Anyway, good fun. But now it’s time for me to walk my two dogs, and then head off to work.



“Worlds Beyond: Science-Fantasy Fiction” magazine lasted only three issues, from December 1950 through February 1951. The January 1951 issue (in the center), featured a cover story with an alien tree where the decision to avoid it is clear.


Demo program. Very long, very complex. Replace “lt” (less than), “gt”, “lte”, “gte” with Boolean operator symbols. (My lame blog editor consistently chokes on symbols).

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

// internal tree: list storage (no pointers),
// stack construct, split minimize quasi-MSE

namespace GradientBoostRegression
{
  internal class GradientBoostRegressionProgram
  {
    static void Main(string[] args)
    {
      Console.WriteLine("\nBegin C# Gradient Boosting" +
        " regression demo ");
      Console.WriteLine("Using list tree ");

      // 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,
        [5], ',', "#"));

      string testFile =
        "..\\..\\..\\Data\\synthetic_test_40.txt";
      double[][] testX =
        MatLoad(testFile, colsX, ',', "#");
      double[] testY =
        MatToVec(MatLoad(testFile,
        [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 numTrees = 100;
      int maxDepth = 3;
      int minSamples = 2;
      int minLeaf = 1;
      double lrnRate = 0.10;  // 0.975 0.800

      Console.WriteLine("\nSetting numTrees = " +
        numTrees);
      Console.WriteLine("Setting maxDepth = " +
        maxDepth);
      Console.WriteLine("Setting minSamples = " +
        minSamples);
      Console.WriteLine("Setting minLeaf = " +
        minLeaf);
      Console.WriteLine("Setting lrnRate = " +
        lrnRate.ToString("F4"));

      Console.WriteLine("\nCreating and training" +
        " GradientBoostRegression model ");
      GradientBoostRegressor gbr =
        new GradientBoostRegressor(numTrees, maxDepth,
        minSamples, minLeaf, lrnRate);
      gbr.Train(trainX, trainY);
      Console.WriteLine("Done ");

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

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

      double r2Train = gbr.R2(trainX, trainY);
      Console.WriteLine("\nR2 train = " +
        r2Train.ToString("F4"));
      double r2Test = gbr.R2(testX, testY);
      Console.WriteLine("R2 test = " +
        r2Test.ToString("F4"));

      // 4. use model
      double[] x = trainX[0];
      Console.WriteLine("\nPredicting for x = ");
      VecShow(x, 4, 9);
      double predY = gbr.Predict(x, verbose: true);
      Console.WriteLine("Predicted 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[][] mat)
    {
      int nRows = mat.Length;
      int nCols = mat[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++] = mat[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 GradientBoostRegressor
  {
    public double lrnRate;
    public int nTrees;
    public int maxDepth;
    public int minSamples;
    public int minLeaf;
    public List"lt"DecisionTreeRegressor"gt" trees;
    public double pred0;  // initial prediction

    public GradientBoostRegressor(int nTrees, int maxDepth,
      int minSamples, int minLeaf, double lrnRate)
    {
      this.nTrees = nTrees;
      this.maxDepth = maxDepth;
      this.minSamples = minSamples;
      this.minLeaf = minLeaf;
      this.trees = new List"lt"DecisionTreeRegressor"gt"();
      this.lrnRate = lrnRate;
    }

    public void Train(double[][] trainX, double[] trainY)
    {
      int n = trainX.Length;
      this.pred0 = Mean(trainY);

      double[] preds = new double[n]; //each data item
      for (int i = 0; i "lt" n; ++i)
        preds[i] = this.pred0;

      for (int t = 0; t "lt" this.nTrees; ++t) // each tree
      {
        double[] residuals = new double[n]; // for curr tree
        for (int i = 0; i "lt" n; ++i)
          residuals[i] = preds[i] - trainY[i];

        DecisionTreeRegressor dtr =
          new DecisionTreeRegressor(this.maxDepth,
          this.minSamples, this.minLeaf);
        dtr.Train(trainX, residuals); // predict residuals

        for (int i = 0; i "lt" n; ++i)
        {
          double predResidual = dtr.Predict(trainX[i]);
          preds[i] -= this.lrnRate * predResidual;
        }
        this.trees.Add(dtr);
      }
    } // Train

    public double Predict(double[] x, bool verbose = false)
    {
      double result = this.pred0;
      if (verbose == true)
      {
        Console.WriteLine("\nInitial prediction: " +
        result.ToString("F4"));
      }
      for (int t = 0; t "lt" this.nTrees; ++t)
      {
        double predResidual = this.trees[t].Predict(x);
        double delta = -this.lrnRate * predResidual;
        result += delta;

        if (verbose == true)
        {
          if (t "gte" 0 && t "lte" 4 || 
            t "gte" this.nTrees - 2 &&
            t "lte" this.nTrees - 1)
          {
            Console.Write("t = " + t.ToString().PadLeft(3) +
              "  pred_res = " + predResidual.ToString("F4").
              PadLeft(7));
            Console.Write("  delta = " + delta.ToString("F4").
              PadLeft(7));
            Console.WriteLine("  pred = " +
              result.ToString("F4").PadLeft(7));
          }
          if (t == 5)
            Console.WriteLine(". . . ");
        }
      }
      return result;
    }

    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 = Predict(dataX[i]);
        if (Math.Abs(predY - actualY) "lt"
          (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;
    }

    public double R2(double[][] dataX, double[] dataY)
    {
      // coefficient of determination
      int n = dataX.Length;
      double sum = 0.0;

      for (int i = 0; i "lt" n; ++i)
        sum += dataY[i];
      double meanActual = sum / n;

      double sumTop = 0.0;
      double sumBot = 0.0;
      for (int i = 0; i "lt" n; ++i)
      {
        double predY = this.Predict(dataX[i]);
        sumTop += (dataY[i] - predY) * (dataY[i] - predY);
        sumBot += (dataY[i] - meanActual) *
          (dataY[i] - meanActual);
      }
      return 1.0 - (sumTop / sumBot);
    }

    private static double Mean(double[] data)
    {
      int n = data.Length;
      double sum = 0.0;
      for (int i = 0; i "lt" n; ++i)
        sum += data[i];
      return sum / n;
    }

  } // class GradientBoostRegression

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

  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 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 Node(int id, int colIdx,
        double thresh, int left, int right,
        double value, bool isLeaf)
      {
        this.id = id;
        this.colIdx = colIdx;
        this.thresh = thresh;
        this.left = left;
        this.right = right;
        this.value = value;
        this.isLeaf = isLeaf;
      }

    } // class Node

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

    public class StackInfo  // used to build tree
    {
      // tree node + associated rows
      public Node node;
      public double[][] dataX;
      public double[] dataY;
      public int depth;

      public StackInfo(Node n, double[][] X,
        double[] y, int d)
      {
        this.node = n; this.dataX = X;
        this.dataY = y; this.depth = d;
      }
    }

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

    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 dummy nodes
      int numNodes = (int)Math.Pow(2, (maxDepth + 1)) - 1;
      for (int i = 0; i "lt" numNodes; ++i)
      {
        // this.tree.Add(null); // OK, but let's avoid ptrs
        Node n = new Node(i, -1, 0.0, -1, -1, 0.0, false);
        this.tree.Add(n); // dummy node
      }
      this.rnd = new Random(seed);
    }

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

    private double[] BestSplit(double[][] dataX,
      double[] dataY)
    {
      // implicit params numSplitCols, minLeaf
      // result[0] = best col idx (as double)
      // result[1] = best split value

      int bestColIdx = -1;  // indicates bad split
      double bestThresh = 0.0;
      double bestMSE = double.MaxValue;  // smaller is better
      int nRows = dataX.Length;  // or dataY.Length
      int nCols = dataX[0].Length;

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

      int[] colIndices = new int[nCols];
      for (int k = 0; k "lt" nCols; ++k)
        colIndices[k] = k;
      Shuffle(colIndices, this.rnd);

      if (this.numSplitCols != -1)  // use only some cols
      {
        int[] cpyIndices = new int[nCols];
        for (int k = 0; k "lt" nCols; ++k)
          cpyIndices[k] = colIndices[k];
        colIndices = new int[this.numSplitCols];
        for (int k = 0; k "lt" this.numSplitCols; ++k)
          colIndices[k] = cpyIndices[k];
      }

      for (int j = 0; j "lt" colIndices.Length; ++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 threh been seen, skip it
          double thresh = dataX[i][colIdx];
          if (examineds.Contains(thresh)) continue;

          examineds.Add(thresh);

          // get rows 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 r = 0; r "lt" nRows; ++r)
          {
            if (dataX[r][colIdx] "lte" thresh)
              leftIdxs.Add(r);
            else
              rightIdxs.Add(r);
          }

          // Check if proposed split would lead to an empty
          // node, which would cause Mean() to fail
          // when building the tree.
          // But allow a node with a single value.
          // if (leftIdxs.Count == 0 ||
          //   rightIdxs.Count == 0)
          //   continue; // scikit "min_samples_leaf=1"
          if (leftIdxs.Count "lt" this.minLeaf ||
            rightIdxs.Count "lt" this.minLeaf)
            continue; // scikit "min_samples_leaf=1"

          // get the left y values and right y values
          List"lt"double"gt" leftValues = 
            new List"lt"double"gt"();
          for (int k = 0; k "lt" leftIdxs.Count; ++k)
            leftValues.Add(dataY[leftIdxs[k]]);

          List"lt"double"gt" rightValues = 
            new List"lt"double"gt"();
          for (int k = 0; k "lt" rightIdxs.Count; ++k)
            rightValues.Add(dataY[rightIdxs[k]]);

          // compute MSE, equivalent to variance reduction
          double mseLeft = MSE(leftValues);
          double mseRight = MSE(rightValues);
          double splitMSE = (leftValues.Count * mseLeft +
            rightValues.Count * mseRight) / nRows;

          if (splitMSE "lt" bestMSE)
          {
            bestColIdx = colIdx;
            bestThresh = thresh;
            bestMSE = splitMSE;
          }

        } // each row
      } // j each col

      double[] result = new double[2];
      result[0] = 1.0 * bestColIdx;
      result[1] = bestThresh;
      return result;

    } // BestSplit()

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

    private static void Shuffle(int[] indices, Random rnd)
    {
      int n = indices.Length;
      for (int i = 0; i "lt" n; ++i)
      {
        int ri = rnd.Next(i, n);
        int tmp = indices[i];
        indices[i] = indices[ri];
        indices[ri] = tmp;
      }
    }

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

    private static double Mean(List"lt"double"gt" values)
    {
      double sum = 0.0;
      for (int i = 0; i "lt" values.Count; ++i)
        sum += values[i];
      return sum / values.Count;
    }

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

    private static double MSE(List"lt"double"gt" values)
    {
      double mean = Mean(values);
      double sum = 0.0;
      for (int i = 0; i "lt" values.Count; ++i)
        sum += (values[i] - mean) * (values[i] - mean);
      return sum / values.Count;
    }

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

    private void MakeTree(double[][] dataX,
      double[] dataY, int depth = 0)
    {
      // no recursion, no pointers, List storage

      Node root = new Node(0, -1, 0.0, 1, 2,
        Mean(dataY.ToList()), false);
      
      Stack"lt"StackInfo"gt" stack = 
        new Stack"lt"StackInfo"gt"();

      stack.Push(new StackInfo(root, dataX, dataY, 0));
      while (stack.Count "gt" 0)
      {
        StackInfo info = stack.Pop();
        Node currNode = info.node;
        this.tree[currNode.id] = currNode;

        double[][] currX = info.dataX;
        double[] currY = info.dataY;
        int currDepth = info.depth;

        if (currDepth == this.maxDepth ||
          currY.Length "lt" this.minSamples) {
          currNode.value = Mean(currY.ToList());
          currNode.isLeaf = true;
          continue;
        }

        double[] splitInfo = this.BestSplit(currX, currY);
        int colIdx = (int)splitInfo[0];
        double thresh = splitInfo[1];

        if (colIdx == -1)  // unable to split
        {
          currNode.value = Mean(currY.ToList());
          currNode.isLeaf = true;
          continue;
        }

        // got a good split so at an internal, non-leaf node
        currNode.colIdx = colIdx;
        currNode.thresh = thresh;

        // make the data splits for children
        List"lt"int"gt" leftIdxs = new List"lt"int"gt"();
        List"lt"int"gt" rightIdxs = new List"lt"int"gt"();
        for (int r = 0; r "lt" currX.Length; ++r)
        {
          if (currX[r][colIdx] "lte" thresh)
            leftIdxs.Add(r);
          else
            rightIdxs.Add(r);
        }

        double[][] leftX = 
          this.ExtractRows(currX, leftIdxs);
        double[] leftY = 
          this.ExtractVals(currY, leftIdxs);
        double[][] rightX = 
          this.ExtractRows(currX, rightIdxs);
        double[] rightY = 
          this.ExtractVals(currY, rightIdxs);

        int leftID = currNode.id * 2 + 1;
        //Node currNodeLeft = new Node(leftID, -1, 0.0,
        //  2*leftID + 1, 2 * leftID + 2, 0.0, false);
        Node currNodeLeft = new Node(leftID, -1, 0.0,
          2*leftID + 1, 2 * leftID + 2,
          Mean(leftY.ToList()), false); // not necessary
        stack.Push(new StackInfo(currNodeLeft, leftX,
          leftY, currDepth + 1));

        int rightID = currNode.id * 2 + 2;
        //Node currNodeRight = new Node(rightID, -1, 0.0,
        //  2*rightID + 1, 2 * rightID + 2, 0.0, false);
        Node currNodeRight = new Node(rightID, -1, 0.0,
          2*rightID + 1, 2 * rightID + 2,
          Mean(rightY.ToList()), false);
        stack.Push(new StackInfo(currNodeRight, rightX,
          rightY, currDepth + 1));
 
      } // while

      return;

    } // MakeTree()

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

    private double[][] ExtractRows(double[][] source,
      List"lt"int"gt" rowIdxs)
    {
      // surprisingly tricky
      int numSrcRows = source.Length;
      int numSrcCols = source[0].Length;
      int numDestRows = rowIdxs.Count;
      int numDestCols = numSrcCols;

      double[][] result = new double[numDestRows][];
      for (int i = 0; i "lt" numDestRows; ++i)
        result[i] = new double[numDestCols];

      for (int i = 0; i "lt" rowIdxs.Count; ++i)
      {
        int srcRow = rowIdxs[i];
        for (int j = 0; j "lt" numDestCols; ++j)
          result[i][j] = source[srcRow][j];
      }
      return result;
    }

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

    private double[] ExtractVals(double[] source,
      List"lt"int"gt" idxs)
    {
      double[] result = new double[idxs.Count];
      for (int i = 0; i "lt" idxs.Count; ++i)
      {
        int srcIdx = idxs[i];
        result[i] = source[srcIdx];
      }
      return result;
    }

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

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

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

    public double Predict(double[] x)
    {
      int p = 0;
      Node currNode = this.tree[p];
      while (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;

    }

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

  } // 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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