Package jline.util.matrix

Class RowView

java.lang.Object
jline.util.matrix.RowView
public class RowView extends Object
A lightweight view into a row of a sparse matrix that doesn't copy data. This provides efficient access to matrix row elements without the overhead of creating a new Matrix object and copying all the data.

This is particularly useful for large sparse matrices where you need to access row elements frequently, such as in iterative algorithms.

Example usage:

 Matrix bigMatrix = ...; // 1000 x 1M sparse matrix
 RowView row = bigMatrix.getRowView(5);

 // Efficient access - only processes non-zero elements
 for (int i = 0; i invalid input: '<' row.getNonZeroCount(); i++) {
     int col = row.getNonZeroCol(i);
     double value = row.getNonZeroValue(i);
     // process (col, value) pair
 }

 // Or get any element (returns 0.0 for non-stored elements)
 double val = row.get(100);
Since:
1.0
Author:
QORE Lab, Imperial College London

  • Method Summary

    Modifier and Type
    Method
    Description
    double
    dotProduct(Matrix columnVector)
    Computes the dot product of this row with a column vector.
    double
    get(int col)
    Returns the value at the specified column in this row.
    int
    getNonZeroCol(int i)
    Returns the column index of the i-th non-zero element in this row.
    int
    getNonZeroCount()
    Returns the number of non-zero elements in this row.
    double
    getNonZeroValue(int i)
    Returns the value of the i-th non-zero element in this row.
    int
    getNumCols()
    Returns the total number of columns in the row (including zeros).
    int
    getRowIndex()
    Returns the row index that this view represents.
    boolean
    hasNonZeros()
    Checks if this row has any non-zero elements.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Method Details

    • dotProduct

      public double dotProduct(Matrix columnVector)
      Computes the dot product of this row with a column vector. This is optimized to only iterate through the non-zero elements of the row.
      Parameters:
      columnVector - the column vector to multiply with (must have getNumRows() == this.getNumCols())
      Returns:
      the scalar result of the dot product
      Throws:
      IllegalArgumentException - if dimensions don't match

    • get

      public double get(int col)
      Returns the value at the specified column in this row. This method searches through the non-zero elements, so it's O(nnz_in_row). For frequent access to multiple elements, consider using the non-zero iterators.
      Parameters:
      col - the column index
      Returns:
      the value at (row, col), or 0.0 if not stored

    • getNonZeroCol

      public int getNonZeroCol(int i)
      Returns the column index of the i-th non-zero element in this row.
      Parameters:
      i - the index into the non-zero elements (0 to getNonZeroCount()-1)
      Returns:
      the column index

    • getNonZeroCount

      public int getNonZeroCount()
      Returns the number of non-zero elements in this row.
      Returns:
      the count of non-zero elements

    • getNonZeroValue

      public double getNonZeroValue(int i)
      Returns the value of the i-th non-zero element in this row.
      Parameters:
      i - the index into the non-zero elements (0 to getNonZeroCount()-1)
      Returns:
      the value

    • getNumCols

      public int getNumCols()
      Returns the total number of columns in the row (including zeros).
      Returns:
      the number of columns

    • getRowIndex

      public int getRowIndex()
      Returns the row index that this view represents.
      Returns:
      the row index

    • hasNonZeros

      public boolean hasNonZeros()
      Checks if this row has any non-zero elements.
      Returns:
      true if the row contains at least one non-zero element