Beispiel #1
0
  @Test
  public void testInverse2x2() {
    double tol = 0.001;
    Map<Key, Value> input = new TreeMap<>(TestUtil.COMPARE_KEY_TO_COLQ);
    input.put(new Key("1", "", "1"), new Value("4".getBytes()));
    input.put(new Key("1", "", "2"), new Value("3".getBytes()));
    input.put(new Key("2", "", "1"), new Value("1".getBytes()));
    input.put(new Key("2", "", "2"), new Value("1".getBytes()));
    Map<Key, Value> expect = new TreeMap<>(TestUtil.COMPARE_KEY_TO_COLQ);
    expect.put(new Key("1", "", "1"), new Value("1 ".getBytes()));
    expect.put(new Key("1", "", "2"), new Value("-3".getBytes()));
    expect.put(new Key("2", "", "1"), new Value("-1".getBytes()));
    expect.put(new Key("2", "", "2"), new Value("4 ".getBytes()));

    RealMatrix matrix = MemMatrixUtil.buildMatrix(input.entrySet().iterator(), 2);
    Assert.assertEquals(2, matrix.getRowDimension());
    Assert.assertEquals(2, matrix.getColumnDimension());
    Assert.assertEquals(4, matrix.getEntry(0, 0), tol);
    Assert.assertEquals(3, matrix.getEntry(0, 1), tol);
    Assert.assertEquals(1, matrix.getEntry(1, 0), tol);
    Assert.assertEquals(1, matrix.getEntry(1, 1), tol);

    matrix = MemMatrixUtil.doInverse(matrix, -1);
    Assert.assertEquals(2, matrix.getRowDimension());
    Assert.assertEquals(2, matrix.getColumnDimension());
    Assert.assertEquals(1, matrix.getEntry(0, 0), tol);
    Assert.assertEquals(-3, matrix.getEntry(0, 1), tol);
    Assert.assertEquals(-1, matrix.getEntry(1, 0), tol);
    Assert.assertEquals(4, matrix.getEntry(1, 1), tol);

    SortedMap<Key, Value> back =
        MemMatrixUtil.matrixToMap(new TreeMap<Key, Value>(TestUtil.COMPARE_KEY_TO_COLQ), matrix);
    TestUtil.assertEqualDoubleMap(expect, back);
  }
  /**
   * Calculates {@code P(D_n < d)} using method described in [1] and doubles (see above).
   *
   * @param d statistic
   * @return the two-sided probability of {@code P(D_n < d)}
   * @throws MathArithmeticException if algorithm fails to convert {@code h} to a {@link
   *     org.apache.commons.math3.fraction.BigFraction} in expressing {@code d} as {@code (k - h) /
   *     m} for integer {@code k, m} and {@code 0 <= h < 1}.
   */
  private double roundedK(double d) throws MathArithmeticException {

    final int k = (int) FastMath.ceil(n * d);
    final FieldMatrix<BigFraction> HBigFraction = this.createH(d);
    final int m = HBigFraction.getRowDimension();

    /*
     * Here the rounding part comes into play: use
     * RealMatrix instead of FieldMatrix<BigFraction>
     */
    final RealMatrix H = new Array2DRowRealMatrix(m, m);

    for (int i = 0; i < m; ++i) {
      for (int j = 0; j < m; ++j) {
        H.setEntry(i, j, HBigFraction.getEntry(i, j).doubleValue());
      }
    }

    final RealMatrix Hpower = H.power(n);

    double pFrac = Hpower.getEntry(k - 1, k - 1);

    for (int i = 1; i <= n; ++i) {
      pFrac *= (double) i / (double) n;
    }

    return pFrac;
  }
  private static Intersection getIntersection(Ray ray, SphereObject obj, Model model) {
    RealMatrix transform = obj.getTransform();
    final RealMatrix transformInverse = obj.getTransformInverse();
    ray = ray.transform(transformInverse);
    Vector3D c = VectorUtils.toVector3D(obj.getCenter());
    Vector3D p0 = VectorUtils.toVector3D(ray.getP0());
    Vector3D p1 = VectorUtils.toVector3D(ray.getP1());
    float a = (float) p1.dotProduct(p1);
    Vector3D p0c = p0.subtract(c);
    float b = (float) p1.dotProduct(p0c) * 2.0f;

    float cc = (float) (p0c.dotProduct(p0c)) - obj.getSize() * obj.getSize();
    Double t = quadraticEquationRoot1(a, b, cc);
    if (t == null || t < EPSILON) {
      return new Intersection(false);
    }
    Intersection result = new Intersection(true);
    result.setObject(obj);
    final Vector3D p = p0.add(p1.scalarMultiply(t));
    RealVector pv = VectorUtils.toRealVector(p);
    pv.setEntry(3, 1.0);
    RealVector pt = transform.preMultiply(pv);
    result.setP(VectorUtils.toVector3D(pt));
    RealVector nv = pv.subtract(obj.getCenter());
    final RealVector nvt = transformInverse.transpose().preMultiply(nv);
    result.setN(VectorUtils.toVector3D(nvt).normalize());
    result.setDistance(t);
    return result;
  }
 @Override
 public Label predict(Instance instance) {
   Label l = null;
   if (instance.getLabel() instanceof ClassificationLabel || instance.getLabel() == null) {
     // ----------------- declare variables ------------------
     double lambda = 0.0;
     RealVector x_instance = new ArrayRealVector(matrixX.getColumnDimension(), 0);
     double result = 0.0;
     // -------------------------- initialize xi -------------------------
     for (int idx = 0; idx < matrixX.getColumnDimension(); idx++) {
       x_instance.setEntry(idx, instance.getFeatureVector().get(idx + 1));
     }
     // ------------------ get lambda -----------------------
     for (int j = 0; j < alpha.getDimension(); j++) {
       lambda += alpha.getEntry(j) * kernelFunction(matrixX.getRowVector(j), x_instance);
     }
     // ----------------- make prediction -----------------
     Sigmoid g = new Sigmoid(); // helper function
     result = g.value(lambda);
     l = new ClassificationLabel(result < 0.5 ? 0 : 1);
   } else {
     System.out.println("label type error!");
   }
   return l;
 }
Beispiel #5
0
  /**
   * @param weight Weight matrix.
   * @throws NonSquareMatrixException if the argument is not a square matrix.
   */
  public Weight(RealMatrix weight) {
    if (weight.getColumnDimension() != weight.getRowDimension()) {
      throw new NonSquareMatrixException(weight.getColumnDimension(), weight.getRowDimension());
    }

    weightMatrix = weight.copy();
  }
Beispiel #6
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  public static RealMatrix stochasticSubmatrix(RealMatrix data, int batch_size, Random rng) {
    // assume all data has the size number_samples by number_features
    int num_samples = data.getRowDimension();
    int num_features = data.getColumnDimension();
    int batch_num = num_samples / batch_size + 1;

    // randomly generate a batch index
    int batch_index = rng.nextInt(batch_num);
    List<Integer> rowIndex_tmp = new ArrayList<Integer>();

    for (int i = 0; i < batch_size; i++) {
      if (batch_size * batch_index + i >= num_samples) {
        break;
      } else {
        rowIndex_tmp.add(batch_size * batch_index + i);
      }
    }
    int[] rowIndex = TypeConvert.ArrayTointv(rowIndex_tmp);

    // System.out.println(rowIndex_tmp);
    int[] columnIndex = new int[num_features];
    for (int j = 0; j < num_features; j++) {
      columnIndex[j] = j;
    }

    // System.out.println(batch_index);

    // return null;
    return data.getSubMatrix(rowIndex, columnIndex);
  }
  /**
   * Build a rating matrix from the rating data. Each user's ratings are first normalized by
   * subtracting a baseline score (usually a mean).
   *
   * @param userMapping The index mapping of user IDs to column numbers.
   * @param itemMapping The index mapping of item IDs to row numbers.
   * @return A matrix storing the <i>normalized</i> user ratings.
   */
  private RealMatrix createRatingMatrix(IdIndexMapping userMapping, IdIndexMapping itemMapping) {
    final int nusers = userMapping.size();
    final int nitems = itemMapping.size();

    // Create a matrix with users on rows and items on columns
    logger.info("creating {} by {} rating matrix", nusers, nitems);
    RealMatrix matrix = MatrixUtils.createRealMatrix(nusers, nitems);

    // populate it with data
    Cursor<UserHistory<Event>> users = userEventDAO.streamEventsByUser();
    try {
      for (UserHistory<Event> user : users) {
        // Get the row number for this user
        int u = userMapping.getIndex(user.getUserId());
        MutableSparseVector ratings = Ratings.userRatingVector(user.filter(Rating.class));
        MutableSparseVector baselines = MutableSparseVector.create(ratings.keySet());
        baselineScorer.score(user.getUserId(), baselines);
        // TODO Populate this user's row with their ratings, minus the baseline scores
        for (VectorEntry entry : ratings.fast(State.SET)) {
          long itemid = entry.getKey();
          int i = itemMapping.getIndex(itemid);
          double rating = entry.getValue();
          double baseline = baselines.get(itemid);
          matrix.setEntry(u, i, rating - baseline);
        }
      }
    } finally {
      users.close();
    }

    return matrix;
  }
Beispiel #8
0
 private List<Integer> findZeroColumns(RealMatrix base) {
   List<Integer> indices = new ArrayList<>();
   for (int i = 0; i < base.getColumnDimension(); i++) {
     if (base.getColumnVector(i).getNorm() == 0) indices.add(i);
   }
   return indices;
 }
  private static RealMatrix S2(double t) {
    double Omega = 73.6667 + 0.013958 * (Times.MJD(t) + 3242) / 365.25;
    double theta0 =
        Math.atan(
            Math.toRadians(
                Math.cos(Math.toRadians(7.25)) * Math.tan(Math.toRadians(lambda0(t) - Omega))));
    double angle1 = (lambda0(t) - Omega);

    angle1 = angle1 % 360.0;
    theta0 = theta0 % 360.0;

    if (angle1 < 0.0) angle1 += 360.0;
    if (theta0 < 0.0) theta0 += 360.0;
    if (angle1 < 180.0) {
      if (theta0 < 180.0) theta0 += 180.0;
    }
    if (angle1 > 180.0) {
      if (theta0 > 180.0) theta0 -= 180.0;
    }

    RealMatrix A = RotationMatrix(theta0, new Vector3D(0, 0, 1));
    RealMatrix B = RotationMatrix(7.25, new Vector3D(1, 0, 0));
    RealMatrix C = RotationMatrix(Omega, new Vector3D(0, 0, 1));
    RealMatrix S2 = A.preMultiply(B).preMultiply(C);
    return S2;
  }
Beispiel #10
0
  private float derivEfAlpha(int i) {
    float res = 0.0f, xIn, yIn, xA, yA, tmp;

    for (int j = 0; j < k; j++) {
      xIn = (float) inputFeatPts.getEntry(j, 0);
      yIn = (float) inputFeatPts.getEntry(j, 1);
      xA = (float) averageFeatPts.getEntry(j, 0);
      yA = (float) averageFeatPts.getEntry(j, 1);

      tmp = 0.0f;
      for (int a = 0; a < 60; a++) {
        // tmp += alpha[a] * (subFSV[a][j][0] + subFSV[a][j][2]);
        tmp +=
            alpha[a]
                * (s[(landmarks83Index[j] - 1) * 3][a] + s[(landmarks83Index[j] - 1) * 3 + 2][a]);
      }
      res +=
          -2.0f
              * ((xIn + yIn) - (xA + yA) - tmp)
              * alpha[i]
              // * (subFSV[i][j][0] + subFSV[i][j][2]);
              * (s[(landmarks83Index[j] - 1) * 3][i] + s[(landmarks83Index[j] - 1) * 3 + 2][i]);
    }
    return res;
  }
 public WeightedLeastSquaresMethod(RealMatrix R, int nFactors, RotationMethod rotationMethod) {
   this.nVariables = R.getColumnDimension();
   this.nParam = nVariables;
   this.nFactors = nFactors;
   this.rotationMethod = rotationMethod;
   this.R = R;
   this.R2 = R.copy();
 }
Beispiel #12
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 /**
  * Throws MathIllegalArgumentException if the matrix does not have at least two columns and two
  * rows.
  *
  * @param matrix matrix to check for sufficiency
  * @throws MathIllegalArgumentException if there is insufficient data
  */
 private void checkSufficientData(final RealMatrix matrix) {
   int nRows = matrix.getRowDimension();
   int nCols = matrix.getColumnDimension();
   if (nRows < 2 || nCols < 2) {
     throw new MathIllegalArgumentException(
         LocalizedFormats.INSUFFICIENT_ROWS_AND_COLUMNS, nRows, nCols);
   }
 }
 public double sumMatrix(RealMatrix matrix) {
   double sum = 0.0;
   for (int i = 0; i < matrix.getRowDimension(); i++) {
     for (int j = 0; j < matrix.getColumnDimension(); j++) {
       sum += matrix.getEntry(i, j);
     }
   }
   return sum;
 }
Beispiel #14
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 /////////////////////////////////// Equation 18 ////////////////////////////////////////////////
 private float computeEf() {
   float res = 0.0f;
   for (int j = 0; j < k; j++) {
     res +=
         pow(inputFeatPts.getEntry(j, 0) - modelFeatPts.getEntry(j, 0), 2)
             + pow(inputFeatPts.getEntry(j, 1) - modelFeatPts.getEntry(j, 1), 2);
   }
   return res;
 }
 public double[][] residuals() {
   double[][] resid = new double[nItems][nItems];
   for (int i = 0; i < SIGMA.getRowDimension(); i++) {
     for (int j = 0; j < SIGMA.getColumnDimension(); j++) {
       resid[i][j] = varcov.getEntry(i, j) - SIGMA.getEntry(i, j);
     }
   }
   return resid;
 }
 /*Transformation matrices*/
 private static RealMatrix P(double t) {
   double t0 = Times.T0(t);
   double zA = 0.64062 * t0 + 0.00030 * Math.pow(t0, 2);
   double thetaA = 0.55675 * t0 + 0.00012 * Math.pow(t0, 2);
   double zetaA = 0.64062 * t0 + 0.00008 * Math.pow(t0, 2);
   RealMatrix A = RotationMatrix(zA, new Vector3D(0, 0, 1));
   RealMatrix B = RotationMatrix(thetaA, new Vector3D(0, 1, 0));
   RealMatrix C = RotationMatrix(zetaA, new Vector3D(0, 0, 1));
   return A.preMultiply(B).preMultiply(C);
 }
 private static RealMatrix T5(double t) {
   double latangle = Math.toDegrees(magnetic_latitude(t)) - 90.0;
   double lonangle = Math.toDegrees(magnetic_longitude(t));
   RealMatrix A =
       RotationMatrix(
           -latangle, new Vector3D(0, 1, 0)); // latangle in original. Change due to java.
   RealMatrix B = RotationMatrix(lonangle, new Vector3D(0, 0, 1));
   RealMatrix T5 = A.preMultiply(B);
   return T5;
 }
Beispiel #18
0
  @Test
  public void testInverseIdentity() {
    double tol = 0.00001;
    Map<Key, Value> input = new TreeMap<>(TestUtil.COMPARE_KEY_TO_COLQ);
    input.put(new Key("1", "", "1"), new Value("1".getBytes()));
    //    input.put(new Key("1", "", "2"), new Value("1".getBytes()));
    //    input.put(new Key("2", "", "1"), new Value("1".getBytes()));
    input.put(new Key("2", "", "2"), new Value("1".getBytes()));

    RealMatrix matrix = MemMatrixUtil.buildMatrix(input.entrySet().iterator(), 2);
    Assert.assertEquals(2, matrix.getRowDimension());
    Assert.assertEquals(2, matrix.getColumnDimension());
    Assert.assertEquals(1, matrix.getEntry(0, 0), tol);
    Assert.assertEquals(0, matrix.getEntry(0, 1), tol);
    Assert.assertEquals(0, matrix.getEntry(1, 0), tol);
    Assert.assertEquals(1, matrix.getEntry(1, 1), tol);

    matrix = MemMatrixUtil.doInverse(matrix, -1);
    Assert.assertEquals(2, matrix.getRowDimension());
    Assert.assertEquals(2, matrix.getColumnDimension());
    Assert.assertEquals(1, matrix.getEntry(0, 0), tol);
    Assert.assertEquals(0, matrix.getEntry(0, 1), tol);
    Assert.assertEquals(0, matrix.getEntry(1, 0), tol);
    Assert.assertEquals(1, matrix.getEntry(1, 1), tol);

    SortedMap<Key, Value> back =
        MemMatrixUtil.matrixToMap(new TreeMap<Key, Value>(TestUtil.COMPARE_KEY_TO_COLQ), matrix);
    TestUtil.assertEqualDoubleMap(input, back);
    //    Assert.assertEquals(1, Double.parseDouble(new String(back.get(new Key("1", "",
    // "1")).get())), tol);
    //    Assert.assertEquals(1, Double.parseDouble(new String(back.get(new Key("2", "",
    // "2")).get())), tol);
  }
 public double meanSquaredResidual() {
   double ni = Double.valueOf(nItems).doubleValue();
   double temp = 0.0, sum = 0.0;
   for (int i = 0; i < SIGMA.getRowDimension(); i++) {
     for (int j = 0; j < SIGMA.getColumnDimension(); j++) {
       temp = varcov.getEntry(i, j) - SIGMA.getEntry(i, j);
       sum += temp * temp;
     }
   }
   return sum / (ni * ni);
 }
 public double[][] squaredResiduals() {
   double[][] resid = new double[nItems][nItems];
   double temp = 0.0;
   for (int i = 0; i < SIGMA.getRowDimension(); i++) {
     for (int j = 0; j < SIGMA.getColumnDimension(); j++) {
       temp = varcov.getEntry(i, j) - SIGMA.getEntry(i, j);
       resid[i][j] = temp * temp;
     }
   }
   return resid;
 }
 public double sumSquaredElements(RealMatrix matrix) {
   double sum = 0.0;
   double v = 0.0;
   for (int i = 0; i < matrix.getRowDimension(); i++) {
     for (int j = 0; j < matrix.getColumnDimension(); j++) {
       v = matrix.getEntry(i, j);
       sum += (v * v);
     }
   }
   return sum;
 }
Beispiel #22
0
 /**
  * Returns a matrix of standard errors associated with the estimates in the correlation matrix.
  * <br>
  * <code>getCorrelationStandardErrors().getEntry(i,j)</code> is the standard error associated with
  * <code>getCorrelationMatrix.getEntry(i,j)</code>
  *
  * <p>The formula used to compute the standard error is <br>
  * <code>SE<sub>r</sub> = ((1 - r<sup>2</sup>) / (n - 2))<sup>1/2</sup></code> where <code>r
  * </code> is the estimated correlation coefficient and <code>n</code> is the number of
  * observations in the source dataset.
  *
  * <p>To use this method, one of the constructors that supply an input matrix must have been used
  * to create this instance.
  *
  * @return matrix of correlation standard errors
  * @throws NullPointerException if this instance was created with no data
  */
 public RealMatrix getCorrelationStandardErrors() {
   int nVars = correlationMatrix.getColumnDimension();
   double[][] out = new double[nVars][nVars];
   for (int i = 0; i < nVars; i++) {
     for (int j = 0; j < nVars; j++) {
       double r = correlationMatrix.getEntry(i, j);
       out[i][j] = FastMath.sqrt((1 - r * r) / (nObs - 2));
     }
   }
   return new BlockRealMatrix(out);
 }
  public static RealMatrix getRealMatrixFromJamaMatrix(Matrix m) {
    final int rDim = m.getRowDimension();
    final int cDim = m.getColumnDimension();
    RealMatrix rm = new Array2DRowRealMatrix(rDim, cDim);
    for (int i = 0; i < rDim; i++) {
      for (int j = 0; j < cDim; j++) {
        rm.setEntry(i, j, m.get(i, j));
      }
    }

    return rm;
  }
  /**
   * @return A matrix containing the row stochastic values of the matrix that contains the
   *     information about the item categorization transposed, to be used by a {@code
   *     HIRItemScorer}.
   */
  public RealMatrix ColumnStochastic() {

    for (int i = 0; i < genreSize; i++) {
      RealVector forIter = transposed.getRowVector(i);
      double sum = forIter.getL1Norm();
      if (sum != 0) {
        forIter.mapDivideToSelf(sum);
        transposed.setRowVector(i, forIter);
      }
    }

    return transposed;
  }
 private double prediction(long user, long item) {
   double baseline = baselineScorer.score(user, item);
   try {
     RealMatrix userFeature = model.getUserVector(user);
     RealMatrix featureWeights = model.getFeatureWeights();
     RealMatrix itemFeature = model.getItemVector(item);
     double product =
         userFeature.multiply(featureWeights).multiply(itemFeature.transpose()).getEntry(0, 0);
     return baseline + product;
   } catch (NullPointerException npe) {
     return baseline;
   }
 }
 public RealMatrix makeZta(RealMatrix userFeature, RealMatrix articleFeature) {
   RealMatrix product = userFeature.multiply(articleFeature.transpose());
   double[][] productData = product.getData();
   double[] productVector = new double[36];
   int count = 0;
   for (int row = 0; row < 6; row++) {
     for (int col = 0; col < 6; col++) {
       productVector[count] = productData[row][col];
       count++;
     }
   }
   return MatrixUtils.createColumnRealMatrix(productVector);
 }
  /**
   * Function to perform QR decomposition on a given matrix.
   *
   * @param in matrix object
   * @return array of matrix blocks
   * @throws DMLRuntimeException if DMLRuntimeException occurs
   */
  private static MatrixBlock[] computeQR(MatrixObject in) throws DMLRuntimeException {
    Array2DRowRealMatrix matrixInput = DataConverter.convertToArray2DRowRealMatrix(in);

    // Perform QR decomposition
    QRDecomposition qrdecompose = new QRDecomposition(matrixInput);
    RealMatrix H = qrdecompose.getH();
    RealMatrix R = qrdecompose.getR();

    // Read the results into native format
    MatrixBlock mbH = DataConverter.convertToMatrixBlock(H.getData());
    MatrixBlock mbR = DataConverter.convertToMatrixBlock(R.getData());

    return new MatrixBlock[] {mbH, mbR};
  }
  /**
   * Build the SVD model.
   *
   * @return A singular value decomposition recommender model.
   */
  @Override
  public SVDModel get() {
    // Create index mappings of user and item IDs.
    // You can use these to find row and columns in the matrix based on user/item IDs.
    IdIndexMapping userMapping = IdIndexMapping.create(userDAO.getUserIds());
    logger.debug("indexed {} users", userMapping.size());
    IdIndexMapping itemMapping = IdIndexMapping.create(itemDAO.getItemIds());
    logger.debug("indexed {} items", itemMapping.size());

    // We have to do 2 things:
    // First, prepare a matrix containing the rating data.
    RealMatrix matrix = createRatingMatrix(userMapping, itemMapping);

    // Second, compute its factorization
    // All the work is done in the constructor
    SingularValueDecomposition svd = new SingularValueDecomposition(matrix);

    // Third, truncate the decomposed matrix
    // TODO Truncate the matrices and construct the SVD model
    RealMatrix userMatrix = svd.getU();
    RealMatrix weights = svd.getS();
    RealMatrix itemMatrix = svd.getV();

    userMatrix = userMatrix.getSubMatrix(0, userMatrix.getRowDimension() - 1, 0, featureCount - 1);
    weights = weights.getSubMatrix(0, featureCount - 1, 0, featureCount - 1);
    itemMatrix = itemMatrix.getSubMatrix(0, itemMatrix.getRowDimension() - 1, 0, featureCount - 1);

    return new SVDModel(userMapping, itemMapping, userMatrix, itemMatrix, weights);
  }
  /**
   * Function to compute Cholesky decomposition of the given input matrix. The input must be a real
   * symmetric positive-definite matrix.
   *
   * @param in commons-math3 Array2DRowRealMatrix
   * @return matrix block
   * @throws DMLRuntimeException if DMLRuntimeException occurs
   */
  private static MatrixBlock computeCholesky(Array2DRowRealMatrix in) throws DMLRuntimeException {
    if (!in.isSquare())
      throw new DMLRuntimeException(
          "Input to cholesky() must be square matrix -- given: a "
              + in.getRowDimension()
              + "x"
              + in.getColumnDimension()
              + " matrix.");

    CholeskyDecomposition cholesky = new CholeskyDecomposition(in);
    RealMatrix rmL = cholesky.getL();

    return DataConverter.convertToMatrixBlock(rmL.getData());
  }
 private static double[] calculateColumnInverseMeans(RealMatrix matrix) {
   return IntStream.range(0, matrix.getColumnDimension())
       .mapToDouble(
           i ->
               1.0
                   / IntStream.range(0, matrix.getRowDimension())
                       .mapToDouble(j -> matrix.getEntry(j, i))
                       .average()
                       .orElseThrow(
                           () ->
                               new IllegalArgumentException(
                                   "cannot calculate a average for column " + i)))
       .toArray();
 }