private GroupBoundsLeastEnlarged pickNext(IList <IBoundable <IExtents> > entries,
ComputationExtents group1Bounds,
ComputationExtents group2Bounds,
out IBoundable <IExtents> entry)
{
Double maxArealDifference = -1;
GroupBoundsLeastEnlarged group = GroupBoundsLeastEnlarged.Tie;
IBoundable <IExtents> nextEntry = null;
foreach (IBoundable <IExtents> e in entries)
{
ComputationExtents bounds = new ComputationExtents(e.Bounds);
ComputationExtents group1Join = bounds.Union(group1Bounds);
ComputationExtents group2Join = bounds.Union(group2Bounds);
Double arealDifferenceGroup1 = Math.Abs(
group1Join.Area - group1Bounds.Area);
Double arealDifferenceGroup2 = Math.Abs(
group2Join.Area - group2Bounds.Area);
Double differenceInAreas = Math.Abs(arealDifferenceGroup1 - arealDifferenceGroup2);
if (differenceInAreas > maxArealDifference)
{
maxArealDifference = differenceInAreas;
nextEntry = e;
if (arealDifferenceGroup1 < arealDifferenceGroup2)
{
group = GroupBoundsLeastEnlarged.Group1;
}
else if (arealDifferenceGroup2 < arealDifferenceGroup1)
{
group = GroupBoundsLeastEnlarged.Group2;
}
}
}
entries.Remove(nextEntry);
entry = nextEntry;
return(group);
}
private GroupBoundsLeastEnlarged pickNext(IList <IBoundable <TBounds> > entries,
TBounds group1Bounds,
TBounds group2Bounds,
out TItem entry)
{
Double maxArealDifference = -1;
GroupBoundsLeastEnlarged group = GroupBoundsLeastEnlarged.Tie;
TItem nextEntry = default(TItem);
foreach (TItem e in entries)
{
TBounds bounds = (TBounds)e.Bounds.Clone();
TBounds group1Join = (TBounds)bounds.Union(group1Bounds);
TBounds group2Join = (TBounds)bounds.Union(group2Bounds);
Double arealDifferenceGroup1 = Math.Abs(
Area(group1Join) - Area(group1Bounds));
Double arealDifferenceGroup2 = Math.Abs(
Area(group2Join) - Area(group2Bounds));
Double differenceInAreas = Math.Abs(arealDifferenceGroup1 - arealDifferenceGroup2);
if (differenceInAreas > maxArealDifference)
{
maxArealDifference = differenceInAreas;
nextEntry = e;
if (arealDifferenceGroup1 < arealDifferenceGroup2)
{
group = GroupBoundsLeastEnlarged.Group1;
}
else if (arealDifferenceGroup2 < arealDifferenceGroup1)
{
group = GroupBoundsLeastEnlarged.Group2;
}
}
}
entries.Remove(nextEntry);
entry = nextEntry;
return(group);
}
private void distribute(IList <IBoundable <IExtents> > entries,
IBoundable <IExtents>[] group1,
IBoundable <IExtents>[] group2,
IndexBalanceHeuristic heuristic,
ref Int32 group1Count,
ref Int32 group2Count)
{
// recursion halting case #1
if (entries.Count == 0)
{
return;
}
// recursion halting case #2
if (group1Count == heuristic.TargetNodeCount ||
group2Count == heuristic.TargetNodeCount)
{
return;
}
IBoundable <IExtents> entry;
ComputationExtents group1Bounds = computeBounds(group1, group1Count);
ComputationExtents group2Bounds = computeBounds(group2, group2Count);
GroupBoundsLeastEnlarged group = pickNext(entries, group1Bounds,
group2Bounds, out entry);
switch (group)
{
case GroupBoundsLeastEnlarged.Group1:
group1[group1Count++] = entry;
break;
case GroupBoundsLeastEnlarged.Group2:
group2[group2Count++] = entry;
break;
case GroupBoundsLeastEnlarged.Tie:
Double group1BoundsArea = group1Bounds.Area;
Double group2BoundsArea = group2Bounds.Area;
if (group1BoundsArea < group2BoundsArea)
{
group1[group1Count++] = entry;
}
else if (group2BoundsArea < group1BoundsArea)
{
group2[group2Count++] = entry;
}
else if (group1Count < group2Count)
{
group1[group1Count++] = entry;
}
else if (group2Count < group1Count)
{
group2[group2Count++] = entry;
}
else if (_random.Next(0, 2) == 0) // generates 0 or 1 randomly
{
group1[group1Count++] = entry;
}
else
{
group2[group2Count++] = entry;
}
break;
default:
throw new InvalidOperationException("Unknown group.");
}
distribute(entries, group1, group2, heuristic, ref group1Count, ref group2Count);
}