AbstractRealMatrix (Apache Commons Math 3.6.1 API)

org.apache.commons.math3.linear

## Class AbstractRealMatrix

- java.lang.Object
- - org.apache.commons.math3.linear.RealLinearOperator
  - - org.apache.commons.math3.linear.AbstractRealMatrix

- All Implemented Interfaces:
    AnyMatrix, RealMatrix
  Direct Known Subclasses:
    Array2DRowRealMatrix, BlockRealMatrix, DiagonalMatrix, OpenMapRealMatrix

      public abstract class AbstractRealMatrix
      extends RealLinearOperator
      implements RealMatrix

  Basic implementation of RealMatrix methods regardless of the underlying storage.

  All the methods implemented here use `getEntry(int, int)` to access matrix elements. Derived class can provide faster implementations.

  Since:
    2.0

- - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `AbstractRealMatrix()` Creates a matrix with no data
    `protected` | `AbstractRealMatrix(int rowDimension, int columnDimension)` Create a new RealMatrix with the supplied row and column dimensions.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `RealMatrix` | `add(RealMatrix m)` Returns the sum of `this` and `m`.
    `void` | `addToEntry(int row, int column, double increment)` Adds (in place) the specified value to the specified entry of `this` matrix.
    `abstract RealMatrix` | `copy()` Returns a (deep) copy of this.
    `void` | `copySubMatrix(int[] selectedRows, int[] selectedColumns, double[][] destination)` Copy a submatrix.
    `void` | `copySubMatrix(int startRow, int endRow, int startColumn, int endColumn, double[][] destination)` Copy a submatrix.
    `abstract RealMatrix` | `createMatrix(int rowDimension, int columnDimension)` Create a new RealMatrix of the same type as the instance with the supplied row and column dimensions.
    `boolean` | `equals(Object object)` Returns true iff `object` is a `RealMatrix` instance with the same dimensions as this and all corresponding matrix entries are equal.
    `double[]` | `getColumn(int column)` Get the entries at the given column index as an array.
    `abstract int` | `getColumnDimension()` Returns the number of columns of this matrix.
    `RealMatrix` | `getColumnMatrix(int column)` Get the entries at the given column index as a column matrix.
    `RealVector` | `getColumnVector(int column)` Get the entries at the given column index as a vector.
    `double[][]` | `getData()` Returns matrix entries as a two-dimensional array.
    `abstract double` | `getEntry(int row, int column)` Get the entry in the specified row and column.
    `double` | `getFrobeniusNorm()` Returns the Frobenius norm of the matrix.
    `double` | `getNorm()` Returns the maximum absolute row sum norm of the matrix.
    `double[]` | `getRow(int row)` Get the entries at the given row index.
    `abstract int` | `getRowDimension()` Returns the number of rows of this matrix.
    `RealMatrix` | `getRowMatrix(int row)` Get the entries at the given row index as a row matrix.
    `RealVector` | `getRowVector(int row)` Returns the entries in row number `row` as a vector.
    `RealMatrix` | `getSubMatrix(int[] selectedRows, int[] selectedColumns)` Gets a submatrix.
    `RealMatrix` | `getSubMatrix(int startRow, int endRow, int startColumn, int endColumn)` Gets a submatrix.
    `double` | `getTrace()` Returns the trace of the matrix (the sum of the elements on the main diagonal).
    `int` | `hashCode()` Computes a hashcode for the matrix.
    `boolean` | `isSquare()` Is this a square matrix?
    `RealMatrix` | `multiply(RealMatrix m)` Returns the result of postmultiplying `this` by `m`.
    `void` | `multiplyEntry(int row, int column, double factor)` Multiplies (in place) the specified entry of `this` matrix by the specified value.
    `double[]` | `operate(double[] v)` Returns the result of multiplying this by the vector `v`.
    `RealVector` | `operate(RealVector v)` Returns the result of multiplying `this` by the vector `x`.
    `RealMatrix` | `power(int p)` Returns the result of multiplying `this` with itself `p` times.
    `double[]` | `preMultiply(double[] v)` Returns the (row) vector result of premultiplying this by the vector `v`.
    `RealMatrix` | `preMultiply(RealMatrix m)` Returns the result of premultiplying `this` by `m`.
    `RealVector` | `preMultiply(RealVector v)` Returns the (row) vector result of premultiplying this by the vector `v`.
    `RealMatrix` | `scalarAdd(double d)` Returns the result of adding `d` to each entry of `this`.
    `RealMatrix` | `scalarMultiply(double d)` Returns the result of multiplying each entry of `this` by `d`.
    `void` | `setColumn(int column, double[] array)` Sets the specified `column` of `this` matrix to the entries of the specified `array`.
    `void` | `setColumnMatrix(int column, RealMatrix matrix)` Sets the specified `column` of `this` matrix to the entries of the specified column `matrix`.
    `void` | `setColumnVector(int column, RealVector vector)` Sets the specified `column` of `this` matrix to the entries of the specified `vector`.
    `abstract void` | `setEntry(int row, int column, double value)` Set the entry in the specified row and column.
    `void` | `setRow(int row, double[] array)` Sets the specified `row` of `this` matrix to the entries of the specified `array`.
    `void` | `setRowMatrix(int row, RealMatrix matrix)` Sets the specified `row` of `this` matrix to the entries of the specified row `matrix`.
    `void` | `setRowVector(int row, RealVector vector)` Sets the specified `row` of `this` matrix to the entries of the specified `vector`.
    `void` | `setSubMatrix(double[][] subMatrix, int row, int column)` Replace the submatrix starting at `row, column` using data in the input `subMatrix` array.
    `RealMatrix` | `subtract(RealMatrix m)` Returns `this` minus `m`.
    `String` | `toString()` Get a string representation for this matrix.
    `RealMatrix` | `transpose()` Returns the transpose of this matrix.
    `double` | `walkInColumnOrder(RealMatrixChangingVisitor visitor)` Visit (and possibly change) all matrix entries in column order.
    `double` | `walkInColumnOrder(RealMatrixChangingVisitor visitor, int startRow, int endRow, int startColumn, int endColumn)` Visit (and possibly change) some matrix entries in column order.
    `double` | `walkInColumnOrder(RealMatrixPreservingVisitor visitor)` Visit (but don't change) all matrix entries in column order.
    `double` | `walkInColumnOrder(RealMatrixPreservingVisitor visitor, int startRow, int endRow, int startColumn, int endColumn)` Visit (but don't change) some matrix entries in column order.
    `double` | `walkInOptimizedOrder(RealMatrixChangingVisitor visitor)` Visit (and possibly change) all matrix entries using the fastest possible order.
    `double` | `walkInOptimizedOrder(RealMatrixChangingVisitor visitor, int startRow, int endRow, int startColumn, int endColumn)` Visit (and possibly change) some matrix entries using the fastest possible order.
    `double` | `walkInOptimizedOrder(RealMatrixPreservingVisitor visitor)` Visit (but don't change) all matrix entries using the fastest possible order.
    `double` | `walkInOptimizedOrder(RealMatrixPreservingVisitor visitor, int startRow, int endRow, int startColumn, int endColumn)` Visit (but don't change) some matrix entries using the fastest possible order.
    `double` | `walkInRowOrder(RealMatrixChangingVisitor visitor)` Visit (and possibly change) all matrix entries in row order.
    `double` | `walkInRowOrder(RealMatrixChangingVisitor visitor, int startRow, int endRow, int startColumn, int endColumn)` Visit (and possibly change) some matrix entries in row order.
    `double` | `walkInRowOrder(RealMatrixPreservingVisitor visitor)` Visit (but don't change) all matrix entries in row order.
    `double` | `walkInRowOrder(RealMatrixPreservingVisitor visitor, int startRow, int endRow, int startColumn, int endColumn)` Visit (but don't change) some matrix entries in row order.

    - ### Methods inherited from class org.apache.commons.math3.linear.RealLinearOperator

      `isTransposable, operateTranspose`

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### AbstractRealMatrix

          protected AbstractRealMatrix()

      Creates a matrix with no data

    - #### AbstractRealMatrix

          protected AbstractRealMatrix(int rowDimension,
                            int columnDimension)
                                throws NotStrictlyPositiveException

      Create a new RealMatrix with the supplied row and column dimensions.
      Parameters:
        `rowDimension` - the number of rows in the new matrix
        `columnDimension` - the number of columns in the new matrix
      Throws:
        `NotStrictlyPositiveException` - if row or column dimension is not positive

  - ### Method Detail

    - #### add

          public RealMatrix add(RealMatrix m)
                         throws MatrixDimensionMismatchException

      Returns the sum of `this` and `m`.
      Specified by:
        `add` in interface `RealMatrix`
      Parameters:
        `m` - matrix to be added
      Returns:
        `this + m`
      Throws:
        `MatrixDimensionMismatchException` - if `m` is not the same size as `this`.

    - #### subtract

          public RealMatrix subtract(RealMatrix m)
                              throws MatrixDimensionMismatchException

      Returns `this` minus `m`.
      Specified by:
        `subtract` in interface `RealMatrix`
      Parameters:
        `m` - matrix to be subtracted
      Returns:
        `this - m`
      Throws:
        `MatrixDimensionMismatchException` - if `m` is not the same size as `this`.

    - #### scalarAdd

          public RealMatrix scalarAdd(double d)

      Returns the result of adding `d` to each entry of `this`.
      Specified by:
        `scalarAdd` in interface `RealMatrix`
      Parameters:
        `d` - value to be added to each entry
      Returns:
        `d + this`

    - #### scalarMultiply

          public RealMatrix scalarMultiply(double d)

      Returns the result of multiplying each entry of `this` by `d`.
      Specified by:
        `scalarMultiply` in interface `RealMatrix`
      Parameters:
        `d` - value to multiply all entries by
      Returns:
        `d * this`

    - #### multiply

          public RealMatrix multiply(RealMatrix m)
                              throws DimensionMismatchException

      Returns the result of postmultiplying `this` by `m`.
      Specified by:
        `multiply` in interface `RealMatrix`
      Parameters:
        `m` - matrix to postmultiply by
      Returns:
        `this * m`
      Throws:
        `DimensionMismatchException` - if `columnDimension(this) != rowDimension(m)`

    - #### preMultiply

          public RealMatrix preMultiply(RealMatrix m)
                                 throws DimensionMismatchException

      Returns the result of premultiplying `this` by `m`.
      Specified by:
        `preMultiply` in interface `RealMatrix`
      Parameters:
        `m` - matrix to premultiply by
      Returns:
        `m * this`
      Throws:
        `DimensionMismatchException` - if `rowDimension(this) != columnDimension(m)`

    - #### power

          public RealMatrix power(int p)
                           throws NotPositiveException,
                                  NonSquareMatrixException

      Returns the result of multiplying `this` with itself `p` times. Depending on the underlying storage, instability for high powers might occur.
      Specified by:
        `power` in interface `RealMatrix`
      Parameters:
        `p` - raise `this` to power `p`
      Returns:
        `this^p`
      Throws:
        `NotPositiveException` - if `p < 0`
        `NonSquareMatrixException` - if the matrix is not square

    - #### getData

          public double[][] getData()

      Returns matrix entries as a two-dimensional array.
      Specified by:
        `getData` in interface `RealMatrix`
      Returns:
        2-dimensional array of entries

    - #### getNorm

          public double getNorm()

      Returns the maximum absolute row sum norm of the matrix.
      Specified by:
        `getNorm` in interface `RealMatrix`
      Returns:
        norm

    - #### getFrobeniusNorm

          public double getFrobeniusNorm()

      Returns the Frobenius norm of the matrix.
      Specified by:
        `getFrobeniusNorm` in interface `RealMatrix`
      Returns:
        norm

    - #### getSubMatrix

          public RealMatrix getSubMatrix(int startRow,
                                int endRow,
                                int startColumn,
                                int endColumn)
                                  throws OutOfRangeException,
                                         NumberIsTooSmallException

      Gets a submatrix. Rows and columns are indicated counting from 0 to n-1.
      Specified by:
        `getSubMatrix` in interface `RealMatrix`
      Parameters:
        `startRow` - Initial row index
        `endRow` - Final row index (inclusive)
        `startColumn` - Initial column index
        `endColumn` - Final column index (inclusive)
      Returns:
        The subMatrix containing the data of the specified rows and columns.
      Throws:
        `OutOfRangeException` - if the indices are not valid.
        `NumberIsTooSmallException` - if `endRow < startRow` or `endColumn < startColumn`.

    - #### getSubMatrix

          public RealMatrix getSubMatrix(int[] selectedRows,
                                int[] selectedColumns)
                                  throws NullArgumentException,
                                         NoDataException,
                                         OutOfRangeException

      Gets a submatrix. Rows and columns are indicated counting from 0 to n-1.
      Specified by:
        `getSubMatrix` in interface `RealMatrix`
      Parameters:
        `selectedRows` - Array of row indices.
        `selectedColumns` - Array of column indices.
      Returns:
        The subMatrix containing the data in the specified rows and columns
      Throws:
        `NullArgumentException` - if the row or column selections are `null`
        `NoDataException` - if the row or column selections are empty (zero length).
        `OutOfRangeException` - if the indices are not valid.

    - #### copySubMatrix

          public void copySubMatrix(int startRow,
                           int endRow,
                           int startColumn,
                           int endColumn,
                           double[][] destination)
                             throws OutOfRangeException,
                                    NumberIsTooSmallException,
                                    MatrixDimensionMismatchException

      Copy a submatrix. Rows and columns are indicated counting from 0 to n-1.
      Specified by:
        `copySubMatrix` in interface `RealMatrix`
      Parameters:
        `startRow` - Initial row index
        `endRow` - Final row index (inclusive)
        `startColumn` - Initial column index
        `endColumn` - Final column index (inclusive)
        `destination` - The arrays where the submatrix data should be copied (if larger than rows/columns counts, only the upper-left part will be used)
      Throws:
        `OutOfRangeException` - if the indices are not valid.
        `NumberIsTooSmallException` - if `endRow < startRow` or `endColumn < startColumn`.
        `MatrixDimensionMismatchException` - if the destination array is too small.

    - #### copySubMatrix

          public void copySubMatrix(int[] selectedRows,
                           int[] selectedColumns,
                           double[][] destination)
                             throws OutOfRangeException,
                                    NullArgumentException,
                                    NoDataException,
                                    MatrixDimensionMismatchException

      Copy a submatrix. Rows and columns are indicated counting from 0 to n-1.
      Specified by:
        `copySubMatrix` in interface `RealMatrix`
      Parameters:
        `selectedRows` - Array of row indices.
        `selectedColumns` - Array of column indices.
        `destination` - The arrays where the submatrix data should be copied (if larger than rows/columns counts, only the upper-left part will be used)
      Throws:
        `OutOfRangeException` - if the indices are not valid.
        `NullArgumentException` - if the row or column selections are `null`
        `NoDataException` - if the row or column selections are empty (zero length).
        `MatrixDimensionMismatchException` - if the destination array is too small.

    - #### setSubMatrix

          public void setSubMatrix(double[][] subMatrix,
                          int row,
                          int column)
                            throws NoDataException,
                                   OutOfRangeException,
                                   DimensionMismatchException,
                                   NullArgumentException

      Replace the submatrix starting at `row, column` using data in the input `subMatrix` array. Indexes are 0-based.

      Example:
      Starting with

           1  2  3  4
           5  6  7  8
           9  0  1  2

      and `subMatrix = {{3, 4} {5,6}}`, invoking `setSubMatrix(subMatrix,1,1))` will result in

           1  2  3  4
           5  3  4  8
           9  5  6  2

      Specified by:
        `setSubMatrix` in interface `RealMatrix`
      Parameters:
        `subMatrix` - array containing the submatrix replacement data
        `row` - row coordinate of the top, left element to be replaced
        `column` - column coordinate of the top, left element to be replaced
      Throws:
        `NoDataException` - if `subMatrix` is empty.
        `OutOfRangeException` - if `subMatrix` does not fit into this matrix from element in `(row, column)`.
        `DimensionMismatchException` - if `subMatrix` is not rectangular (not all rows have the same length) or empty.
        `NullArgumentException` - if `subMatrix` is `null`.

    - #### getRowMatrix

          public RealMatrix getRowMatrix(int row)
                                  throws OutOfRangeException

      Get the entries at the given row index as a row matrix. Row indices start at 0.
      Specified by:
        `getRowMatrix` in interface `RealMatrix`
      Parameters:
        `row` - Row to be fetched.
      Returns:
        row Matrix.
      Throws:
        `OutOfRangeException` - if the specified row index is invalid.

    - #### setRowMatrix

          public void setRowMatrix(int row,
                          RealMatrix matrix)
                            throws OutOfRangeException,
                                   MatrixDimensionMismatchException

      Sets the specified `row` of `this` matrix to the entries of the specified row `matrix`. Row indices start at 0.
      Specified by:
        `setRowMatrix` in interface `RealMatrix`
      Parameters:
        `row` - Row to be set.
        `matrix` - Row matrix to be copied (must have one row and the same number of columns as the instance).
      Throws:
        `OutOfRangeException` - if the specified row index is invalid.
        `MatrixDimensionMismatchException` - if the row dimension of the `matrix` is not `1`, or the column dimensions of `this` and `matrix` do not match.

    - #### getColumnMatrix

          public RealMatrix getColumnMatrix(int column)
                                     throws OutOfRangeException

      Get the entries at the given column index as a column matrix. Column indices start at 0.
      Specified by:
        `getColumnMatrix` in interface `RealMatrix`
      Parameters:
        `column` - Column to be fetched.
      Returns:
        column Matrix.
      Throws:
        `OutOfRangeException` - if the specified column index is invalid.

    - #### setColumnMatrix

          public void setColumnMatrix(int column,
                             RealMatrix matrix)
                               throws OutOfRangeException,
                                      MatrixDimensionMismatchException

      Sets the specified `column` of `this` matrix to the entries of the specified column `matrix`. Column indices start at 0.
      Specified by:
        `setColumnMatrix` in interface `RealMatrix`
      Parameters:
        `column` - Column to be set.
        `matrix` - Column matrix to be copied (must have one column and the same number of rows as the instance).
      Throws:
        `OutOfRangeException` - if the specified column index is invalid.
        `MatrixDimensionMismatchException` - if the column dimension of the `matrix` is not `1`, or the row dimensions of `this` and `matrix` do not match.

    - #### getRowVector

          public RealVector getRowVector(int row)
                                  throws OutOfRangeException

      Returns the entries in row number `row` as a vector. Row indices start at 0.
      Specified by:
        `getRowVector` in interface `RealMatrix`
      Parameters:
        `row` - Row to be fetched.
      Returns:
        a row vector.
      Throws:
        `OutOfRangeException` - if the specified row index is invalid.

    - #### setRowVector

          public void setRowVector(int row,
                          RealVector vector)
                            throws OutOfRangeException,
                                   MatrixDimensionMismatchException

      Sets the specified `row` of `this` matrix to the entries of the specified `vector`. Row indices start at 0.
      Specified by:
        `setRowVector` in interface `RealMatrix`
      Parameters:
        `row` - Row to be set.
        `vector` - row vector to be copied (must have the same number of column as the instance).
      Throws:
        `OutOfRangeException` - if the specified row index is invalid.
        `MatrixDimensionMismatchException` - if the `vector` dimension does not match the column dimension of `this` matrix.

    - #### getColumnVector

          public RealVector getColumnVector(int column)
                                     throws OutOfRangeException

      Get the entries at the given column index as a vector. Column indices start at 0.
      Specified by:
        `getColumnVector` in interface `RealMatrix`
      Parameters:
        `column` - Column to be fetched.
      Returns:
        a column vector.
      Throws:
        `OutOfRangeException` - if the specified column index is invalid

    - #### setColumnVector

          public void setColumnVector(int column,
                             RealVector vector)
                               throws OutOfRangeException,
                                      MatrixDimensionMismatchException

      Sets the specified `column` of `this` matrix to the entries of the specified `vector`. Column indices start at 0.
      Specified by:
        `setColumnVector` in interface `RealMatrix`
      Parameters:
        `column` - Column to be set.
        `vector` - column vector to be copied (must have the same number of rows as the instance).
      Throws:
        `OutOfRangeException` - if the specified column index is invalid.
        `MatrixDimensionMismatchException` - if the `vector` dimension does not match the row dimension of `this` matrix.

    - #### getRow

          public double[] getRow(int row)
                          throws OutOfRangeException

      Get the entries at the given row index. Row indices start at 0.
      Specified by:
        `getRow` in interface `RealMatrix`
      Parameters:
        `row` - Row to be fetched.
      Returns:
        the array of entries in the row.
      Throws:
        `OutOfRangeException` - if the specified row index is not valid.

    - #### setRow

          public void setRow(int row,
                    double[] array)
                      throws OutOfRangeException,
                             MatrixDimensionMismatchException

      Sets the specified `row` of `this` matrix to the entries of the specified `array`. Row indices start at 0.
      Specified by:
        `setRow` in interface `RealMatrix`
      Parameters:
        `row` - Row to be set.
        `array` - Row matrix to be copied (must have the same number of columns as the instance)
      Throws:
        `OutOfRangeException` - if the specified row index is invalid.
        `MatrixDimensionMismatchException` - if the `array` length does not match the column dimension of `this` matrix.

    - #### getColumn

          public double[] getColumn(int column)
                             throws OutOfRangeException

      Get the entries at the given column index as an array. Column indices start at 0.
      Specified by:
        `getColumn` in interface `RealMatrix`
      Parameters:
        `column` - Column to be fetched.
      Returns:
        the array of entries in the column.
      Throws:
        `OutOfRangeException` - if the specified column index is not valid.

    - #### setColumn

          public void setColumn(int column,
                       double[] array)
                         throws OutOfRangeException,
                                MatrixDimensionMismatchException

      Sets the specified `column` of `this` matrix to the entries of the specified `array`. Column indices start at 0.
      Specified by:
        `setColumn` in interface `RealMatrix`
      Parameters:
        `column` - Column to be set.
        `array` - Column array to be copied (must have the same number of rows as the instance).
      Throws:
        `OutOfRangeException` - if the specified column index is invalid.
        `MatrixDimensionMismatchException` - if the `array` length does not match the row dimension of `this` matrix.

    - #### addToEntry

          public void addToEntry(int row,
                        int column,
                        double increment)
                          throws OutOfRangeException

      Adds (in place) the specified value to the specified entry of `this` matrix. Row and column indices start at 0.
      Specified by:
        `addToEntry` in interface `RealMatrix`
      Parameters:
        `row` - Row index of the entry to be modified.
        `column` - Column index of the entry to be modified.
        `increment` - value to add to the matrix entry.
      Throws:
        `OutOfRangeException` - if the row or column index is not valid.

    - #### multiplyEntry

          public void multiplyEntry(int row,
                           int column,
                           double factor)
                             throws OutOfRangeException

      Multiplies (in place) the specified entry of `this` matrix by the specified value. Row and column indices start at 0.
      Specified by:
        `multiplyEntry` in interface `RealMatrix`
      Parameters:
        `row` - Row index of the entry to be modified.
        `column` - Column index of the entry to be modified.
        `factor` - Multiplication factor for the matrix entry.
      Throws:
        `OutOfRangeException` - if the row or column index is not valid.

    - #### transpose

          public RealMatrix transpose()

      Returns the transpose of this matrix.
      Specified by:
        `transpose` in interface `RealMatrix`
      Returns:
        transpose matrix

    - #### isSquare

          public boolean isSquare()

      Is this a square matrix?
      Specified by:
        `isSquare` in interface `AnyMatrix`
      Returns:
        true if the matrix is square (rowDimension = columnDimension)

    - #### getRowDimension

          public abstract int getRowDimension()

      Returns the number of rows of this matrix.
      Specified by:
        `getRowDimension` in interface `AnyMatrix`
      Specified by:
        `getRowDimension` in class `RealLinearOperator`
      Returns:
        the number of rows.

    - #### getColumnDimension

          public abstract int getColumnDimension()

      Returns the number of columns of this matrix.
      Specified by:
        `getColumnDimension` in interface `AnyMatrix`
      Specified by:
        `getColumnDimension` in class `RealLinearOperator`
      Returns:
        the number of columns.

    - #### getTrace

          public double getTrace()
                          throws NonSquareMatrixException

      Returns the trace of the matrix (the sum of the elements on the main diagonal).
      Specified by:
        `getTrace` in interface `RealMatrix`
      Returns:
        the trace.
      Throws:
        `NonSquareMatrixException` - if the matrix is not square.

    - #### operate

          public double[] operate(double[] v)
                           throws DimensionMismatchException

      Returns the result of multiplying this by the vector `v`.
      Specified by:
        `operate` in interface `RealMatrix`
      Parameters:
        `v` - the vector to operate on
      Returns:
        `this * v`
      Throws:
        `DimensionMismatchException` - if the length of `v` does not match the column dimension of `this`.

    - #### operate

          public RealVector operate(RealVector v)
                             throws DimensionMismatchException

      Returns the result of multiplying `this` by the vector `x`.
      Specified by:
        `operate` in interface `RealMatrix`
      Specified by:
        `operate` in class `RealLinearOperator`
      Parameters:
        `v` - the vector to operate on
      Returns:
        the product of `this` instance with `x`
      Throws:
        `DimensionMismatchException` - if the column dimension does not match the size of `x`

    - #### preMultiply

          public double[] preMultiply(double[] v)
                               throws DimensionMismatchException

      Returns the (row) vector result of premultiplying this by the vector `v`.
      Specified by:
        `preMultiply` in interface `RealMatrix`
      Parameters:
        `v` - the row vector to premultiply by
      Returns:
        `v * this`
      Throws:
        `DimensionMismatchException` - if the length of `v` does not match the row dimension of `this`.

    - #### preMultiply

          public RealVector preMultiply(RealVector v)
                                 throws DimensionMismatchException

      Returns the (row) vector result of premultiplying this by the vector `v`.
      Specified by:
        `preMultiply` in interface `RealMatrix`
      Parameters:
        `v` - the row vector to premultiply by
      Returns:
        `v * this`
      Throws:
        `DimensionMismatchException` - if the dimension of `v` does not match the row dimension of `this`.

    - #### walkInRowOrder

          public double walkInRowOrder(RealMatrixChangingVisitor visitor)

      Visit (and possibly change) all matrix entries in row order.

      Row order starts at upper left and iterating through all elements of a row from left to right before going to the leftmost element of the next row.

      Specified by:
        `walkInRowOrder` in interface `RealMatrix`
      Parameters:
        `visitor` - visitor used to process all matrix entries
      Returns:
        the value returned by `RealMatrixChangingVisitor.end()` at the end of the walk
      See Also:
        `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor, int, int, int, int)`

    - #### walkInRowOrder

          public double walkInRowOrder(RealMatrixPreservingVisitor visitor)

      Visit (but don't change) all matrix entries in row order.

      Row order starts at upper left and iterating through all elements of a row from left to right before going to the leftmost element of the next row.

      Specified by:
        `walkInRowOrder` in interface `RealMatrix`
      Parameters:
        `visitor` - visitor used to process all matrix entries
      Returns:
        the value returned by `RealMatrixPreservingVisitor.end()` at the end of the walk
      See Also:
        `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor, int, int, int, int)`

    - #### walkInRowOrder

          public double walkInRowOrder(RealMatrixChangingVisitor visitor,
                              int startRow,
                              int endRow,
                              int startColumn,
                              int endColumn)
                                throws OutOfRangeException,
                                       NumberIsTooSmallException

      Visit (and possibly change) some matrix entries in row order.

      Row order starts at upper left and iterating through all elements of a row from left to right before going to the leftmost element of the next row.

      Specified by:
        `walkInRowOrder` in interface `RealMatrix`
      Parameters:
        `visitor` - visitor used to process all matrix entries
        `startRow` - Initial row index
        `endRow` - Final row index (inclusive)
        `startColumn` - Initial column index
        `endColumn` - Final column index
      Returns:
        the value returned by `RealMatrixChangingVisitor.end()` at the end of the walk
      Throws:
        `OutOfRangeException` - if the indices are not valid.
        `NumberIsTooSmallException` - if `endRow < startRow` or `endColumn < startColumn`.
      See Also:
        `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor, int, int, int, int)`

    - #### walkInRowOrder

          public double walkInRowOrder(RealMatrixPreservingVisitor visitor,
                              int startRow,
                              int endRow,
                              int startColumn,
                              int endColumn)
                                throws OutOfRangeException,
                                       NumberIsTooSmallException

      Visit (but don't change) some matrix entries in row order.

      Row order starts at upper left and iterating through all elements of a row from left to right before going to the leftmost element of the next row.

      Specified by:
        `walkInRowOrder` in interface `RealMatrix`
      Parameters:
        `visitor` - visitor used to process all matrix entries
        `startRow` - Initial row index
        `endRow` - Final row index (inclusive)
        `startColumn` - Initial column index
        `endColumn` - Final column index
      Returns:
        the value returned by `RealMatrixPreservingVisitor.end()` at the end of the walk
      Throws:
        `OutOfRangeException` - if the indices are not valid.
        `NumberIsTooSmallException` - if `endRow < startRow` or `endColumn < startColumn`.
      See Also:
        `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor, int, int, int, int)`

    - #### walkInColumnOrder

          public double walkInColumnOrder(RealMatrixChangingVisitor visitor)

      Visit (and possibly change) all matrix entries in column order.

      Column order starts at upper left and iterating through all elements of a column from top to bottom before going to the topmost element of the next column.

      Specified by:
        `walkInColumnOrder` in interface `RealMatrix`
      Parameters:
        `visitor` - visitor used to process all matrix entries
      Returns:
        the value returned by `RealMatrixChangingVisitor.end()` at the end of the walk
      See Also:
        `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor, int, int, int, int)`

    - #### walkInColumnOrder

          public double walkInColumnOrder(RealMatrixPreservingVisitor visitor)

      Visit (but don't change) all matrix entries in column order.

      Column order starts at upper left and iterating through all elements of a column from top to bottom before going to the topmost element of the next column.

      Specified by:
        `walkInColumnOrder` in interface `RealMatrix`
      Parameters:
        `visitor` - visitor used to process all matrix entries
      Returns:
        the value returned by `RealMatrixPreservingVisitor.end()` at the end of the walk
      See Also:
        `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor, int, int, int, int)`

    - #### walkInColumnOrder

          public double walkInColumnOrder(RealMatrixChangingVisitor visitor,
                                 int startRow,
                                 int endRow,
                                 int startColumn,
                                 int endColumn)
                                   throws OutOfRangeException,
                                          NumberIsTooSmallException

      Visit (and possibly change) some matrix entries in column order.

      Column order starts at upper left and iterating through all elements of a column from top to bottom before going to the topmost element of the next column.

      Specified by:
        `walkInColumnOrder` in interface `RealMatrix`
      Parameters:
        `visitor` - visitor used to process all matrix entries
        `startRow` - Initial row index
        `endRow` - Final row index (inclusive)
        `startColumn` - Initial column index
        `endColumn` - Final column index
      Returns:
        the value returned by `RealMatrixChangingVisitor.end()` at the end of the walk
      Throws:
        `OutOfRangeException` - if the indices are not valid.
        `NumberIsTooSmallException` - if `endRow < startRow` or `endColumn < startColumn`.
      See Also:
        `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor, int, int, int, int)`

    - #### walkInColumnOrder

          public double walkInColumnOrder(RealMatrixPreservingVisitor visitor,
                                 int startRow,
                                 int endRow,
                                 int startColumn,
                                 int endColumn)
                                   throws OutOfRangeException,
                                          NumberIsTooSmallException

      Visit (but don't change) some matrix entries in column order.

      Column order starts at upper left and iterating through all elements of a column from top to bottom before going to the topmost element of the next column.

      Specified by:
        `walkInColumnOrder` in interface `RealMatrix`
      Parameters:
        `visitor` - visitor used to process all matrix entries
        `startRow` - Initial row index
        `endRow` - Final row index (inclusive)
        `startColumn` - Initial column index
        `endColumn` - Final column index
      Returns:
        the value returned by `RealMatrixPreservingVisitor.end()` at the end of the walk
      Throws:
        `OutOfRangeException` - if the indices are not valid.
        `NumberIsTooSmallException` - if `endRow < startRow` or `endColumn < startColumn`.
      See Also:
        `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor, int, int, int, int)`

    - #### walkInOptimizedOrder

          public double walkInOptimizedOrder(RealMatrixChangingVisitor visitor)

      Visit (and possibly change) all matrix entries using the fastest possible order.

      The fastest walking order depends on the exact matrix class. It may be different from traditional row or column orders.

      Specified by:
        `walkInOptimizedOrder` in interface `RealMatrix`
      Parameters:
        `visitor` - visitor used to process all matrix entries
      Returns:
        the value returned by `RealMatrixChangingVisitor.end()` at the end of the walk
      See Also:
        `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor, int, int, int, int)`

    - #### walkInOptimizedOrder

          public double walkInOptimizedOrder(RealMatrixPreservingVisitor visitor)

      Visit (but don't change) all matrix entries using the fastest possible order.

      The fastest walking order depends on the exact matrix class. It may be different from traditional row or column orders.

      Specified by:
        `walkInOptimizedOrder` in interface `RealMatrix`
      Parameters:
        `visitor` - visitor used to process all matrix entries
      Returns:
        the value returned by `RealMatrixPreservingVisitor.end()` at the end of the walk
      See Also:
        `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor, int, int, int, int)`

    - #### walkInOptimizedOrder

          public double walkInOptimizedOrder(RealMatrixChangingVisitor visitor,
                                    int startRow,
                                    int endRow,
                                    int startColumn,
                                    int endColumn)
                                      throws OutOfRangeException,
                                             NumberIsTooSmallException

      Visit (and possibly change) some matrix entries using the fastest possible order.

      The fastest walking order depends on the exact matrix class. It may be different from traditional row or column orders.

      Specified by:
        `walkInOptimizedOrder` in interface `RealMatrix`
      Parameters:
        `visitor` - visitor used to process all matrix entries
        `startRow` - Initial row index
        `endRow` - Final row index (inclusive)
        `startColumn` - Initial column index
        `endColumn` - Final column index (inclusive)
      Returns:
        the value returned by `RealMatrixChangingVisitor.end()` at the end of the walk
      Throws:
        `OutOfRangeException` - if the indices are not valid.
        `NumberIsTooSmallException` - if `endRow < startRow` or `endColumn < startColumn`.
      See Also:
        `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor, int, int, int, int)`

    - #### walkInOptimizedOrder

          public double walkInOptimizedOrder(RealMatrixPreservingVisitor visitor,
                                    int startRow,
                                    int endRow,
                                    int startColumn,
                                    int endColumn)
                                      throws OutOfRangeException,
                                             NumberIsTooSmallException

      Visit (but don't change) some matrix entries using the fastest possible order.

      The fastest walking order depends on the exact matrix class. It may be different from traditional row or column orders.

      Specified by:
        `walkInOptimizedOrder` in interface `RealMatrix`
      Parameters:
        `visitor` - visitor used to process all matrix entries
        `startRow` - Initial row index
        `endRow` - Final row index (inclusive)
        `startColumn` - Initial column index
        `endColumn` - Final column index (inclusive)
      Returns:
        the value returned by `RealMatrixPreservingVisitor.end()` at the end of the walk
      Throws:
        `OutOfRangeException` - if the indices are not valid.
        `NumberIsTooSmallException` - if `endRow < startRow` or `endColumn < startColumn`.
      See Also:
        `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInRowOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInRowOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInColumnOrder(RealMatrixChangingVisitor, int, int, int, int)`, `RealMatrix.walkInColumnOrder(RealMatrixPreservingVisitor, int, int, int, int)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixPreservingVisitor)`, `RealMatrix.walkInOptimizedOrder(RealMatrixChangingVisitor, int, int, int, int)`

    - #### toString

          public String toString()

      Get a string representation for this matrix.
      Overrides:
        `toString` in class `Object`
      Returns:
        a string representation for this matrix

    - #### equals

          public boolean equals(Object object)

      Returns true iff `object` is a `RealMatrix` instance with the same dimensions as this and all corresponding matrix entries are equal.
      Overrides:
        `equals` in class `Object`
      Parameters:
        `object` - the object to test equality against.
      Returns:
        true if object equals this

    - #### hashCode

          public int hashCode()

      Computes a hashcode for the matrix.
      Overrides:
        `hashCode` in class `Object`
      Returns:
        hashcode for matrix

    - #### createMatrix

          public abstract RealMatrix createMatrix(int rowDimension,
                                int columnDimension)
                                           throws NotStrictlyPositiveException

      Create a new RealMatrix of the same type as the instance with the supplied row and column dimensions.
      Specified by:
        `createMatrix` in interface `RealMatrix`
      Parameters:
        `rowDimension` - the number of rows in the new matrix
        `columnDimension` - the number of columns in the new matrix
      Returns:
        a new matrix of the same type as the instance
      Throws:
        `NotStrictlyPositiveException` - if row or column dimension is not positive.

    - #### copy

          public abstract RealMatrix copy()

      Returns a (deep) copy of this.
      Specified by:
        `copy` in interface `RealMatrix`
      Returns:
        matrix copy

    - #### getEntry

          public abstract double getEntry(int row,
                        int column)
                                   throws OutOfRangeException

      Get the entry in the specified row and column. Row and column indices start at 0.
      Specified by:
        `getEntry` in interface `RealMatrix`
      Parameters:
        `row` - Row index of entry to be fetched.
        `column` - Column index of entry to be fetched.
      Returns:
        the matrix entry at `(row, column)`.
      Throws:
        `OutOfRangeException` - if the row or column index is not valid.

    - #### setEntry

          public abstract void setEntry(int row,
                      int column,
                      double value)
                                 throws OutOfRangeException

      Set the entry in the specified row and column. Row and column indices start at 0.
      Specified by:
        `setEntry` in interface `RealMatrix`
      Parameters:
        `row` - Row index of entry to be set.
        `column` - Column index of entry to be set.
        `value` - the new value of the entry.
      Throws:
        `OutOfRangeException` - if the row or column index is not valid

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