/// <summary>
/// Modifies the given matrix to be a randomly sampled matrix.
/// Randomly picks exactly <i>System.Math.Round(rows*columns*nonZeroFraction)</i> cells and initializes them to <i>value</i>, all the rest will be initialized to zero.
/// Note that this is not the same as setting each cell with probability <i>nonZeroFraction</i> to <i>value</i>.
/// Note: The random seed is a constant.
/// </summary>
/// <param name="factory"></param>
/// <param name="matrix"></param>
/// <param name="value"></param>
/// <param name="nonZeroFraction"></param>
/// <returns></returns>
/// <exception cref="ArgumentException">if nonZeroFraction < 0 || nonZeroFraction > 1.</exception>
/// <see cref="Cern.Jet.Random.Sampling.RandomSamplingAssistant"/>
public static DoubleMatrix2D Sample(this DoubleFactory2D factory, DoubleMatrix2D matrix, double value, double nonZeroFraction)
{
int rows = matrix.Rows;
int columns = matrix.Columns;
double epsilon = 1e-09;
if (nonZeroFraction < 0 - epsilon || nonZeroFraction > 1 + epsilon)
{
throw new ArgumentException();
}
if (nonZeroFraction < 0)
{
nonZeroFraction = 0;
}
if (nonZeroFraction > 1)
{
nonZeroFraction = 1;
}
matrix.Assign(0);
int size = rows * columns;
int n = (int)System.Math.Round(size * nonZeroFraction);
if (n == 0)
{
return(matrix);
}
var sampler = new Cern.Jet.Random.Sampling.RandomSamplingAssistant(n, size, new Cern.Jet.Random.Engine.MersenneTwister());
for (int i = 0; i < size; i++)
{
if (sampler.SampleNextElement())
{
int row = (int)(i / columns);
int column = (int)(i % columns);
matrix[row, column] = value;
}
}
return(matrix);
}
/// <summary>
/// Constructs a randomly sampled matrix with the given shape.
/// Randomly picks exactly<tt>Math.round(rows* columns* nonZeroFraction)</tt> cells and initializes them to<tt> value</tt>, all the rest will be initialized to zero.
/// Note that this is not the same as setting each cell with probability<tt> nonZeroFraction</tt> to<tt> value</tt>.
/// Note: The random seed is a constant.
/// </summary>
/// <param name="factory"></param>
/// <param name="rows"></param>
/// <param name="columns"></param>
/// <param name="value"></param>
/// <param name="nonZeroFraction"></param>
/// <returns></returns>
/// <exception cref="ArgumentException">if nonZeroFraction < 0 || nonZeroFraction > 1.</exception>
/// <see cref="Cern.Jet.Random.Sampling.RandomSamplingAssistant"/>
public static DoubleMatrix2D Sample(this DoubleFactory2D factory, int rows, int columns, double value, double nonZeroFraction)
{
DoubleMatrix2D matrix = factory.Make(rows, columns);
return(Sample(factory, matrix, value, nonZeroFraction));
}