/// <summary>
/// 9 point stencil operation.
/// Applies a function to a moving <i>3 x 3</i> window.
/// </summary>
/// <param name="A">
/// the matrix to operate on.
/// </param>
/// <param name="function">
/// the function to be applied to each window.
/// </param>
/// <param name="maxIterations">
/// the maximum number of times the stencil shall be applied to the matrixd
/// Should be a multiple of 2 because two iterations are always done in one atomic step.
/// </param>
/// <param name="hasConverged">
/// Convergence condition; will return before maxIterations are done when <i>hasConverged.apply(A)==true</i>.
/// Set this parameter to <i>null</i> to indicate that no convergence checks shall be made.
/// </param>
/// <param name="convergenceIterations">
/// the number of iterations to pass between each convergence check.
/// (Since a convergence may be expensive, you may want to do it only every 2,4 or 8 iterationsd)
/// </param>
/// <returns><the number of iterations actually executedd /returns>
public static int Stencil9(DoubleMatrix2D A, Cern.Colt.Function.Double9Function function, int maxIterations, DoubleMatrix2DProcedure hasConverged, int convergenceIterations)
{
DoubleMatrix2D B = A.Copy();
if (convergenceIterations <= 1)
{
convergenceIterations = 2;
}
if (convergenceIterations % 2 != 0)
{
convergenceIterations++; // odd -> make it even
}
int i = 0;
while (i < maxIterations)
{ // do two steps at a time for efficiency
A.ZAssign8Neighbors(B, function);
B.ZAssign8Neighbors(A, function);
i = i + 2;
if (i % convergenceIterations == 0 && hasConverged != null)
{
if (hasConverged(A))
{
return(i);
}
}
}
return(i);
}