org.apache.commons.math3.linear

## Class SparseFieldVector<T extends FieldElement<T>>

- java.lang.Object
- - org.apache.commons.math3.linear.SparseFieldVector<T>

- Type Parameters:
    `T` - the type of the field elements
  All Implemented Interfaces:
    Serializable, FieldVector<T>

      public class SparseFieldVector<T extends FieldElement<T>>
      extends Object
      implements FieldVector<T>, Serializable

  This class implements the `FieldVector` interface with a `OpenIntToFieldHashMap` backing store.

  Caveat: This implementation assumes that, for any `x`, the equality `x * 0d == 0d` holds. But it is is not true for `NaN`. Moreover, zero entries will lose their sign. Some operations (that involve `NaN` and/or infinities) may thus give incorrect results.

  Since:
    2.0
  See Also:
    Serialized Form

- - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `` | `SparseFieldVector(Field<T> field)` Build a 0-length vector.
    `` | `SparseFieldVector(Field<T> field, int dimension)` Construct a vector of zeroes.
    `` | `SparseFieldVector(Field<T> field, int dimension, int expectedSize)` Build a vector with known the sparseness (for advanced use only).
    `` | `SparseFieldVector(Field<T> field, T[] values)` Create from a Field array.
    `` | `SparseFieldVector(SparseFieldVector<T> v)` Copy constructor.
    `protected` | `SparseFieldVector(SparseFieldVector<T> v, int resize)` Build a resized vector, for use with append.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `FieldVector<T>` | `add(FieldVector<T> v)` Compute the sum of `this` and `v`.
    `FieldVector<T>` | `add(SparseFieldVector<T> v)` Optimized method to add sparse vectors.
    `FieldVector<T>` | `append(FieldVector<T> v)` Construct a vector by appending a vector to this vector.
    `FieldVector<T>` | `append(SparseFieldVector<T> v)` Construct a vector by appending a vector to this vector.
    `FieldVector<T>` | `append(T d)` Construct a vector by appending a T to this vector.
    `protected void` | `checkVectorDimensions(int n)` Check if instance dimension is equal to some expected value.
    `FieldVector<T>` | `copy()` Returns a (deep) copy of this.
    `T` | `dotProduct(FieldVector<T> v)` Compute the dot product.
    `FieldVector<T>` | `ebeDivide(FieldVector<T> v)` Element-by-element division.
    `FieldVector<T>` | `ebeMultiply(FieldVector<T> v)` Element-by-element multiplication.
    `boolean` | `equals(Object obj)`
    `T[]` | `getData()` Deprecated. as of 3.1, to be removed in 4.0. Please use the `toArray()` method instead.
    `int` | `getDimension()` Returns the size of the vector.
    `T` | `getEntry(int index)` Returns the entry in the specified index.
    `Field<T>` | `getField()` Get the type of field elements of the vector.
    `FieldVector<T>` | `getSubVector(int index, int n)` Get a subvector from consecutive elements.
    `int` | `hashCode()`
    `FieldVector<T>` | `mapAdd(T d)` Map an addition operation to each entry.
    `FieldVector<T>` | `mapAddToSelf(T d)` Map an addition operation to each entry.
    `FieldVector<T>` | `mapDivide(T d)` Map a division operation to each entry.
    `FieldVector<T>` | `mapDivideToSelf(T d)` Map a division operation to each entry.
    `FieldVector<T>` | `mapInv()` Map the 1/x function to each entry.
    `FieldVector<T>` | `mapInvToSelf()` Map the 1/x function to each entry.
    `FieldVector<T>` | `mapMultiply(T d)` Map a multiplication operation to each entry.
    `FieldVector<T>` | `mapMultiplyToSelf(T d)` Map a multiplication operation to each entry.
    `FieldVector<T>` | `mapSubtract(T d)` Map a subtraction operation to each entry.
    `FieldVector<T>` | `mapSubtractToSelf(T d)` Map a subtraction operation to each entry.
    `FieldMatrix<T>` | `outerProduct(FieldVector<T> v)` Compute the outer product.
    `FieldMatrix<T>` | `outerProduct(SparseFieldVector<T> v)` Optimized method to compute outer product when both vectors are sparse.
    `FieldVector<T>` | `projection(FieldVector<T> v)` Find the orthogonal projection of this vector onto another vector.
    `void` | `set(T value)` Set all elements to a single value.
    `void` | `setEntry(int index, T value)` Set a single element.
    `void` | `setSubVector(int index, FieldVector<T> v)` Set a set of consecutive elements.
    `FieldVector<T>` | `subtract(FieldVector<T> v)` Compute `this` minus `v`.
    `SparseFieldVector<T>` | `subtract(SparseFieldVector<T> v)` Optimized method to compute `this` minus `v`.
    `T[]` | `toArray()` Convert the vector to a T array.
    `T` | `walkInDefaultOrder(FieldVectorChangingVisitor<T> visitor)` Visits (and possibly alters) all entries of this vector in default order (increasing index).
    `T` | `walkInDefaultOrder(FieldVectorChangingVisitor<T> visitor, int start, int end)` Visits (and possibly alters) some entries of this vector in default order (increasing index).
    `T` | `walkInDefaultOrder(FieldVectorPreservingVisitor<T> visitor)` Visits (but does not alter) all entries of this vector in default order (increasing index).
    `T` | `walkInDefaultOrder(FieldVectorPreservingVisitor<T> visitor, int start, int end)` Visits (but does not alter) some entries of this vector in default order (increasing index).
    `T` | `walkInOptimizedOrder(FieldVectorChangingVisitor<T> visitor)` Visits (and possibly alters) all entries of this vector in optimized order.
    `T` | `walkInOptimizedOrder(FieldVectorChangingVisitor<T> visitor, int start, int end)` Visits (and possibly change) some entries of this vector in optimized order.
    `T` | `walkInOptimizedOrder(FieldVectorPreservingVisitor<T> visitor)` Visits (but does not alter) all entries of this vector in optimized order.
    `T` | `walkInOptimizedOrder(FieldVectorPreservingVisitor<T> visitor, int start, int end)` Visits (but does not alter) some entries of this vector in optimized order.

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

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

- - ### Constructor Detail

    - #### SparseFieldVector

          public SparseFieldVector(Field<T> field)

      Build a 0-length vector. Zero-length vectors may be used to initialize construction of vectors by data gathering. We start with zero-length and use either the `SparseFieldVector(SparseFieldVector, int)` constructor or one of the `append` method (`append(FieldVector)` or `append(SparseFieldVector)`) to gather data into this vector.
      Parameters:
        `field` - Field to which the elements belong.

    - #### SparseFieldVector

          public SparseFieldVector(Field<T> field,
                           int dimension)

      Construct a vector of zeroes.
      Parameters:
        `field` - Field to which the elements belong.
        `dimension` - Size of the vector.

    - #### SparseFieldVector

          protected SparseFieldVector(SparseFieldVector<T> v,
                           int resize)

      Build a resized vector, for use with append.
      Parameters:
        `v` - Original vector
        `resize` - Amount to add.

    - #### SparseFieldVector

          public SparseFieldVector(Field<T> field,
                           int dimension,
                           int expectedSize)

      Build a vector with known the sparseness (for advanced use only).
      Parameters:
        `field` - Field to which the elements belong.
        `dimension` - Size of the vector.
        `expectedSize` - Expected number of non-zero entries.

    - #### SparseFieldVector

          public SparseFieldVector(Field<T> field,
                           T[] values)
                            throws NullArgumentException

      Create from a Field array. Only non-zero entries will be stored.
      Parameters:
        `field` - Field to which the elements belong.
        `values` - Set of values to create from.
      Throws:
        `NullArgumentException` - if values is null

    - #### SparseFieldVector

          public SparseFieldVector(SparseFieldVector<T> v)

      Copy constructor.
      Parameters:
        `v` - Instance to copy.

  - ### Method Detail

    - #### add

          public FieldVector<T> add(SparseFieldVector<T> v)
                                                     throws DimensionMismatchException

      Optimized method to add sparse vectors.
      Parameters:
        `v` - Vector to add.
      Returns:
        `this + v`.
      Throws:
        `DimensionMismatchException` - if `v` is not the same size as `this`.

    - #### append

          public FieldVector<T> append(SparseFieldVector<T> v)

      Construct a vector by appending a vector to this vector.
      Parameters:
        `v` - Vector to append to this one.
      Returns:
        a new vector.

    - #### append

          public FieldVector<T> append(FieldVector<T> v)

      Construct a vector by appending a vector to this vector.
      Specified by:
        `append` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `v` - vector to append to this one.
      Returns:
        a new vector

    - #### append

          public FieldVector<T> append(T d)
                                                        throws NullArgumentException

      Construct a vector by appending a T to this vector.
      Specified by:
        `append` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `d` - T to append.
      Returns:
        a new vector
      Throws:
        `NullArgumentException` - if d is null

    - #### copy

          public FieldVector<T> copy()

      Returns a (deep) copy of this.
      Specified by:
        `copy` in interface `FieldVector<T extends FieldElement<T>>`
      Returns:
        vector copy

    - #### dotProduct

          public T dotProduct(FieldVector<T> v)
                                               throws DimensionMismatchException

      Compute the dot product.
      Specified by:
        `dotProduct` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `v` - vector with which dot product should be computed
      Returns:
        the scalar dot product of `this` and `v`
      Throws:
        `DimensionMismatchException` - if `v` is not the same size as `this`

    - #### ebeDivide

          public FieldVector<T> ebeDivide(FieldVector<T> v)
                                                           throws DimensionMismatchException,
                                                                  MathArithmeticException

      Element-by-element division.
      Specified by:
        `ebeDivide` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `v` - vector by which instance elements must be divided
      Returns:
        a vector containing `this[i] / v[i]` for all `i`
      Throws:
        `DimensionMismatchException` - if `v` is not the same size as `this`
        `MathArithmeticException` - if one entry of `v` is zero.

    - #### ebeMultiply

          public FieldVector<T> ebeMultiply(FieldVector<T> v)
                                                             throws DimensionMismatchException

      Element-by-element multiplication.
      Specified by:
        `ebeMultiply` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `v` - vector by which instance elements must be multiplied
      Returns:
        a vector containing `this[i] * v[i]` for all `i`
      Throws:
        `DimensionMismatchException` - if `v` is not the same size as `this`

    - #### getData

          @Deprecated
          public T[] getData()

      Deprecated. as of 3.1, to be removed in 4.0. Please use the `toArray()` method instead.
      Returns vector entries as a T array.
      Specified by:
        `getData` in interface `FieldVector<T extends FieldElement<T>>`
      Returns:
        T array of entries

    - #### getDimension

          public int getDimension()

      Returns the size of the vector.
      Specified by:
        `getDimension` in interface `FieldVector<T extends FieldElement<T>>`
      Returns:
        size

    - #### getEntry

          public T getEntry(int index)
                                             throws OutOfRangeException

      Returns the entry in the specified index.
      Specified by:
        `getEntry` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `index` - Index location of entry to be fetched.
      Returns:
        the vector entry at `index`.
      Throws:
        `OutOfRangeException` - if the index is not valid.
      See Also:
        `FieldVector.setEntry(int, FieldElement)`

    - #### getField

          public Field<T> getField()

      Get the type of field elements of the vector.
      Specified by:
        `getField` in interface `FieldVector<T extends FieldElement<T>>`
      Returns:
        type of field elements of the vector

    - #### getSubVector

          public FieldVector<T> getSubVector(int index,
                                    int n)
                                                              throws OutOfRangeException,
                                                                     NotPositiveException

      Get a subvector from consecutive elements.
      Specified by:
        `getSubVector` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `index` - index of first element.
        `n` - number of elements to be retrieved.
      Returns:
        a vector containing n elements.
      Throws:
        `OutOfRangeException` - if the index is not valid.
        `NotPositiveException` - if the number of elements if not positive.

    - #### mapAdd

          public FieldVector<T> mapAdd(T d)
                                                        throws NullArgumentException

      Map an addition operation to each entry.
      Specified by:
        `mapAdd` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `d` - value to be added to each entry
      Returns:
        `this + d`
      Throws:
        `NullArgumentException` - if `d` is `null`.

    - #### mapAddToSelf

          public FieldVector<T> mapAddToSelf(T d)
                                                              throws NullArgumentException

      Map an addition operation to each entry.

      The instance is changed by this method.

      Specified by:
        `mapAddToSelf` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `d` - value to be added to each entry
      Returns:
        for convenience, return `this`
      Throws:
        `NullArgumentException` - if `d` is `null`.

    - #### mapDivide

          public FieldVector<T> mapDivide(T d)
                                                           throws NullArgumentException,
                                                                  MathArithmeticException

      Map a division operation to each entry.
      Specified by:
        `mapDivide` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `d` - value to divide all entries by
      Returns:
        `this / d`
      Throws:
        `NullArgumentException` - if `d` is `null`.
        `MathArithmeticException` - if `d` is zero.

    - #### mapDivideToSelf

          public FieldVector<T> mapDivideToSelf(T d)
                                                                 throws NullArgumentException,
                                                                        MathArithmeticException

      Map a division operation to each entry.

      The instance is changed by this method.

      Specified by:
        `mapDivideToSelf` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `d` - value to divide all entries by
      Returns:
        for convenience, return `this`
      Throws:
        `NullArgumentException` - if `d` is `null`.
        `MathArithmeticException` - if `d` is zero.

    - #### mapInv

          public FieldVector<T> mapInv()
                                                        throws MathArithmeticException

      Map the 1/x function to each entry.
      Specified by:
        `mapInv` in interface `FieldVector<T extends FieldElement<T>>`
      Returns:
        a vector containing the result of applying the function to each entry.
      Throws:
        `MathArithmeticException` - if one of the entries is zero.

    - #### mapInvToSelf

          public FieldVector<T> mapInvToSelf()
                                                              throws MathArithmeticException

      Map the 1/x function to each entry.

      The instance is changed by this method.

      Specified by:
        `mapInvToSelf` in interface `FieldVector<T extends FieldElement<T>>`
      Returns:
        for convenience, return `this`
      Throws:
        `MathArithmeticException` - if one of the entries is zero.

    - #### mapMultiply

          public FieldVector<T> mapMultiply(T d)
                                                             throws NullArgumentException

      Map a multiplication operation to each entry.
      Specified by:
        `mapMultiply` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `d` - value to multiply all entries by
      Returns:
        `this * d`
      Throws:
        `NullArgumentException` - if `d` is `null`.

    - #### mapMultiplyToSelf

          public FieldVector<T> mapMultiplyToSelf(T d)
                                                                   throws NullArgumentException

      Map a multiplication operation to each entry.

      The instance is changed by this method.

      Specified by:
        `mapMultiplyToSelf` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `d` - value to multiply all entries by
      Returns:
        for convenience, return `this`
      Throws:
        `NullArgumentException` - if `d` is `null`.

    - #### mapSubtract

          public FieldVector<T> mapSubtract(T d)
                                                             throws NullArgumentException

      Map a subtraction operation to each entry.
      Specified by:
        `mapSubtract` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `d` - value to be subtracted to each entry
      Returns:
        `this - d`
      Throws:
        `NullArgumentException` - if `d` is `null`

    - #### mapSubtractToSelf

          public FieldVector<T> mapSubtractToSelf(T d)
                                                                   throws NullArgumentException

      Map a subtraction operation to each entry.

      The instance is changed by this method.

      Specified by:
        `mapSubtractToSelf` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `d` - value to be subtracted to each entry
      Returns:
        for convenience, return `this`
      Throws:
        `NullArgumentException` - if `d` is `null`

    - #### outerProduct

          public FieldMatrix<T> outerProduct(SparseFieldVector<T> v)

      Optimized method to compute outer product when both vectors are sparse.
      Parameters:
        `v` - vector with which outer product should be computed
      Returns:
        the matrix outer product between instance and v

    - #### outerProduct

          public FieldMatrix<T> outerProduct(FieldVector<T> v)

      Compute the outer product.
      Specified by:
        `outerProduct` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `v` - vector with which outer product should be computed
      Returns:
        the matrix outer product between instance and v

    - #### projection

          public FieldVector<T> projection(FieldVector<T> v)
                                                            throws DimensionMismatchException,
                                                                   MathArithmeticException

      Find the orthogonal projection of this vector onto another vector.
      Specified by:
        `projection` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `v` - vector onto which `this` must be projected
      Returns:
        projection of `this` onto `v`
      Throws:
        `DimensionMismatchException` - if `v` is not the same size as `this`
        `MathArithmeticException` - if `v` is the null vector.

    - #### set

          public void set(T value)

      Set all elements to a single value.
      Specified by:
        `set` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `value` - single value to set for all elements
      Throws:
        `NullArgumentException` - if value is null

    - #### setEntry

          public void setEntry(int index,
                      T value)
                        throws NullArgumentException,
                               OutOfRangeException

      Set a single element.
      Specified by:
        `setEntry` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `index` - element index.
        `value` - new value for the element.
      Throws:
        `NullArgumentException` - if value is null
        `OutOfRangeException` - if the index is not valid.
      See Also:
        `FieldVector.getEntry(int)`

    - #### setSubVector

          public void setSubVector(int index,
                          FieldVector<T> v)
                            throws OutOfRangeException

      Set a set of consecutive elements.
      Specified by:
        `setSubVector` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `index` - index of first element to be set.
        `v` - vector containing the values to set.
      Throws:
        `OutOfRangeException` - if the index is not valid.

    - #### subtract

          public SparseFieldVector<T> subtract(SparseFieldVector<T> v)
                                                                throws DimensionMismatchException

      Optimized method to compute `this` minus `v`.
      Parameters:
        `v` - vector to be subtracted
      Returns:
        `this - v`
      Throws:
        `DimensionMismatchException` - if `v` is not the same size as `this`.

    - #### subtract

          public FieldVector<T> subtract(FieldVector<T> v)
                                                          throws DimensionMismatchException

      Compute `this` minus `v`.
      Specified by:
        `subtract` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `v` - vector to be subtracted
      Returns:
        `this - v`
      Throws:
        `DimensionMismatchException` - if `v` is not the same size as `this`

    - #### toArray

          public T[] toArray()

      Convert the vector to a T array.

      The array is independent from vector data, it's elements are copied.

      Specified by:
        `toArray` in interface `FieldVector<T extends FieldElement<T>>`
      Returns:
        array containing a copy of vector elements

    - #### checkVectorDimensions

          protected void checkVectorDimensions(int n)
                                        throws DimensionMismatchException

      Check if instance dimension is equal to some expected value.
      Parameters:
        `n` - Expected dimension.
      Throws:
        `DimensionMismatchException` - if the dimensions do not match.

    - #### add

          public FieldVector<T> add(FieldVector<T> v)
                                                     throws DimensionMismatchException

      Compute the sum of `this` and `v`.
      Specified by:
        `add` in interface `FieldVector<T extends FieldElement<T>>`
      Parameters:
        `v` - vector to be added
      Returns:
        `this + v`
      Throws:
        `DimensionMismatchException` - if `v` is not the same size as `this`

    - #### walkInDefaultOrder

          public T walkInDefaultOrder(FieldVectorPreservingVisitor<T> visitor)

      Visits (but does not alter) all entries of this vector in default order (increasing index).
      Parameters:
        `visitor` - the visitor to be used to process the entries of this vector
      Returns:
        the value returned by `FieldVectorPreservingVisitor.end()` at the end of the walk
      Since:
        3.3

    - #### walkInDefaultOrder

          public T walkInDefaultOrder(FieldVectorPreservingVisitor<T> visitor,
                             int start,
                             int end)
                                                       throws NumberIsTooSmallException,
                                                              OutOfRangeException

      Visits (but does not alter) some entries of this vector in default order (increasing index).
      Parameters:
        `visitor` - visitor to be used to process the entries of this vector
        `start` - the index of the first entry to be visited
        `end` - the index of the last entry to be visited (inclusive)
      Returns:
        the value returned by `FieldVectorPreservingVisitor.end()` at the end of the walk
      Throws:
        `NumberIsTooSmallException` - if `end < start`.
        `OutOfRangeException` - if the indices are not valid.
      Since:
        3.3

    - #### walkInOptimizedOrder

          public T walkInOptimizedOrder(FieldVectorPreservingVisitor<T> visitor)

      Visits (but does not alter) all entries of this vector in optimized order. The order in which the entries are visited is selected so as to lead to the most efficient implementation; it might depend on the concrete implementation of this abstract class.
      Parameters:
        `visitor` - the visitor to be used to process the entries of this vector
      Returns:
        the value returned by `FieldVectorPreservingVisitor.end()` at the end of the walk
      Since:
        3.3

    - #### walkInOptimizedOrder

          public T walkInOptimizedOrder(FieldVectorPreservingVisitor<T> visitor,
                               int start,
                               int end)
                                                         throws NumberIsTooSmallException,
                                                                OutOfRangeException

      Visits (but does not alter) some entries of this vector in optimized order. The order in which the entries are visited is selected so as to lead to the most efficient implementation; it might depend on the concrete implementation of this abstract class.
      Parameters:
        `visitor` - visitor to be used to process the entries of this vector
        `start` - the index of the first entry to be visited
        `end` - the index of the last entry to be visited (inclusive)
      Returns:
        the value returned by `FieldVectorPreservingVisitor.end()` at the end of the walk
      Throws:
        `NumberIsTooSmallException` - if `end < start`.
        `OutOfRangeException` - if the indices are not valid.
      Since:
        3.3

    - #### walkInDefaultOrder

          public T walkInDefaultOrder(FieldVectorChangingVisitor<T> visitor)

      Visits (and possibly alters) all entries of this vector in default order (increasing index).
      Parameters:
        `visitor` - the visitor to be used to process and modify the entries of this vector
      Returns:
        the value returned by `FieldVectorChangingVisitor.end()` at the end of the walk
      Since:
        3.3

    - #### walkInDefaultOrder

          public T walkInDefaultOrder(FieldVectorChangingVisitor<T> visitor,
                             int start,
                             int end)
                                                       throws NumberIsTooSmallException,
                                                              OutOfRangeException

      Visits (and possibly alters) some entries of this vector in default order (increasing index).
      Parameters:
        `visitor` - visitor to be used to process the entries of this vector
        `start` - the index of the first entry to be visited
        `end` - the index of the last entry to be visited (inclusive)
      Returns:
        the value returned by `FieldVectorChangingVisitor.end()` at the end of the walk
      Throws:
        `NumberIsTooSmallException` - if `end < start`.
        `OutOfRangeException` - if the indices are not valid.
      Since:
        3.3

    - #### walkInOptimizedOrder

          public T walkInOptimizedOrder(FieldVectorChangingVisitor<T> visitor)

      Visits (and possibly alters) all entries of this vector in optimized order. The order in which the entries are visited is selected so as to lead to the most efficient implementation; it might depend on the concrete implementation of this abstract class.
      Parameters:
        `visitor` - the visitor to be used to process the entries of this vector
      Returns:
        the value returned by `FieldVectorChangingVisitor.end()` at the end of the walk
      Since:
        3.3

    - #### walkInOptimizedOrder

          public T walkInOptimizedOrder(FieldVectorChangingVisitor<T> visitor,
                               int start,
                               int end)
                                                         throws NumberIsTooSmallException,
                                                                OutOfRangeException

      Visits (and possibly change) some entries of this vector in optimized order. The order in which the entries are visited is selected so as to lead to the most efficient implementation; it might depend on the concrete implementation of this abstract class.
      Parameters:
        `visitor` - visitor to be used to process the entries of this vector
        `start` - the index of the first entry to be visited
        `end` - the index of the last entry to be visited (inclusive)
      Returns:
        the value returned by `FieldVectorChangingVisitor.end()` at the end of the walk
      Throws:
        `NumberIsTooSmallException` - if `end < start`.
        `OutOfRangeException` - if the indices are not valid.
      Since:
        3.3

    - #### hashCode

          public int hashCode()

      Overrides:
        `hashCode` in class `Object`

    - #### equals

          public boolean equals(Object obj)

      Overrides:
        `equals` in class `Object`

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