/// <summary>
/// Reduces the search space by removing nodes, removing edges and merging nodes.
/// </summary>
/// <returns>The nodes contained in the reduced search space.</returns>
public IReadOnlyList <GraphNode> ReduceSearchSpace()
{
// Remove all non target nodes with 2 or less edges. (Steiner nodes always have more than 2 edges)
var nodeCountBefore = _nodeStates.SearchSpaceSize;
_nodeStates.SearchSpace = _nodeStates.SearchSpace.Where(n => n.Adjacent.Count > 2 || _nodeStates.IsTarget(n)).ToList();
Debug.WriteLine("First basic degree reduction:\n" +
" removed nodes: " + (nodeCountBefore - _nodeStates.SearchSpaceSize) + " (of " + nodeCountBefore +
" initial nodes)");
// Initialise the distance lookup.
_data.DistanceLookup = new DistanceLookup(_nodeStates.SearchSpace);
var distanceLookup = _data.DistanceLookup;
// Distance indices were not set before.
_nodeStates.ComputeFields();
// If a fixed target node is not connected to the start node, there obviously is no solution at all.
if (_nodeStates.FixedTargetNodeIndices.Any(i => !distanceLookup.AreConnected(i, _data.StartNodeIndex)))
{
throw new GraphNotConnectedException();
}
nodeCountBefore = _nodeStates.SearchSpaceSize;
// Remove all unconnected nodes.
_nodeStates.SearchSpace = distanceLookup.RemoveNodes(_nodeStates.SearchSpace.Where(n => !distanceLookup.AreConnected(n, StartNode)));
Debug.WriteLine("Removed unconnected nodes:");
Debug.WriteLine(" removed nodes: " + (nodeCountBefore - _nodeStates.SearchSpaceSize));
// Even the basic degree reductions hurt the AdvancedSolver's performance.
// Reenabling should be tested when other algorithm parts are changed/improved.
// todo experiment with reductions and AdvancedSolver
if (_nodeStates.VariableTargetNodeCount > 0)
{
return(_nodeStates.SearchSpace);
}
// Initialise node states and edges. Edges are calculated from the information in the
// GraphNode. Adjacency information from GraphNode instances must not be used after this.
_data.EdgeSet = ComputeEdges();
var initialNodeCount = _nodeStates.SearchSpaceSize;
var initialEdgeCount = _data.EdgeSet.Count;
Debug.WriteLine("Initial counts:\n"
+ " nodes: " + initialNodeCount + "\n"
+ " non targets: " + (_nodeStates.SearchSpaceSize - _nodeStates.TargetNodeCount) + "\n"
+ " variable targets: " + _nodeStates.VariableTargetNodeCount + "\n"
+ " fixed targets: " + _nodeStates.FixedTargetNodeCount + "\n"
+ " edges: " + initialEdgeCount);
// Execute an initial DegreeTest.
var degreeTest = new DegreeTest(_nodeStates, _data);
var dummy = 0;
degreeTest.RunTest(ref dummy, ref dummy);
// Update _searchSpace, _edgeSet and _distanceLookup
ContractSearchSpace();
// These values may become lower by merging nodes. Since the reductions based on these distance
// don't help if there are many variable target nodes, it is not really worth it to always recalculate them.
// It would either slow the preprocessing by like 30% or would need an approximation algorithm.
_data.SMatrix = new BottleneckSteinerDistanceCalculator(distanceLookup).CalcBottleneckSteinerDistances(_nodeStates.FixedTargetNodeIndices);
// The set of reduction test that are run until they are no longer able to reduce the search space.
var tests = new List <SteinerReduction>
{
new FarAwayNonTerminalsTest(_nodeStates, _data),
new PathsWithManyTerminalsTest(_nodeStates, _data),
new NonTerminalsOfDegreeKTest(_nodeStates, _data),
new NearestVertexTest(_nodeStates, _data)
};
// Run every reduction test (each followed by a simple degree reduction test) until they are no longer able
// to reduce the search space or 10 reduction rounds were executed.
// (the 10 round limit is never actually reached from what I've seen)
for (int i = 0; i < 10; i++)
{
var edgeElims = 0;
var nodeElims = 0;
foreach (var test in tests.Where(t => t.IsEnabled))
{
if (!test.RunTest(ref edgeElims, ref nodeElims))
{
test.IsEnabled = false;
}
degreeTest.RunTest(ref edgeElims, ref nodeElims);
}
Debug.WriteLine("Eliminations in round {0}:", i + 1);
Debug.WriteLine(" removed nodes: " + nodeElims);
Debug.WriteLine(" removed edges: " + edgeElims);
// No test should be still enabled in this case so we can stop running them.
if (edgeElims == 0)
{
break;
}
}
// Calculate the final search space.
ContractSearchSpace();
Debug.WriteLine("Final counts:\n"
+ " nodes: " + _nodeStates.SearchSpaceSize + " (of " + initialNodeCount + " after basic reductions)\n"
+ " non targets: " + (_nodeStates.SearchSpaceSize - _nodeStates.TargetNodeCount) + "\n"
+ " variable targets: " + _nodeStates.VariableTargetNodeCount + "\n"
+ " fixed targets: " + _nodeStates.FixedTargetNodeCount + "\n"
+ " edges: " + _data.EdgeSet.Count + " (of " + initialEdgeCount + " after basic reductions)");
return(_nodeStates.SearchSpace);
}
/// <summary>
/// Reduces the search space by removing nodes, removing edges and merging nodes.
/// </summary>
/// <returns>The nodes contained in the reduced search space.</returns>
public SteinerPreprocessorResult ReduceSearchSpace()
{
// Remove all non target nodes with 2 or less edges. (Steiner nodes always have more than 2 edges)
var nodeCountBefore = _nodeStates.SearchSpaceSize;
_nodeStates.SearchSpace = _nodeStates.SearchSpace.Where(n => n.Adjacent.Count > 2 || _nodeStates.IsTarget(n)).ToList();
Debug.WriteLine("First basic degree reduction:\n" +
" removed nodes: " + (nodeCountBefore - _nodeStates.SearchSpaceSize) + " (of " + nodeCountBefore +
" initial nodes)");
// Initialize the distance lookup.
_data.DistanceCalculator = new DistanceCalculator(_nodeStates.SearchSpace);
var distanceLookup = _data.DistanceCalculator;
#if PoESkillTree_EnableAlternativeFixedTargetNodeIndices
foreach (var node in distanceLookup._nodes.Where(n => _nodeStates.TargetIds.Contains(n.Id)))//Update NodeIndexes
{
if (node.DistancesIndex == -1)
#if DEBUG
{
Debug.WriteLine("Failed to index distance calculations for node:" + node.Id);
#endif
{ _nodeStates.FixedTargetKeyedIndices.Remove(node.Id); //Remove from Dictionary if node has invalid index
}
#if DEBUG
}
#endif
else
{
_nodeStates.FixedTargetKeyedIndices.AddOrUpdate(node.Id, node.DistancesIndex);
}
}
#endif
// Distance indices are set in ComputeFields() if PoESkillTree_DisableAlternativeFixedTargetNodeIndices is enabled.(old variation of the code otherwise Distance indice is updated in ReduceSearchSpace())
_nodeStates.ComputeFields();
// If a fixed target node is not connected to the start node, there obviously is no solution at all.
if (_nodeStates.FixedTargetNodeIndices.Any(i =>
#if PoESkillTree_UseShortDistanceIndex
_data.StartNodeIndex != null &&
#endif
!distanceLookup.AreConnectedById(i,
#if PoESkillTree_UseShortDistanceIndex
(ushort)
#endif
_data.StartNodeIndex)))
{
throw new GraphNotConnectedException();
}
nodeCountBefore = _nodeStates.SearchSpaceSize;
// Remove all unconnected nodes.
_nodeStates.SearchSpace = distanceLookup.RemoveNodes(_nodeStates.SearchSpace.Where(n => !distanceLookup.AreConnected(n, _data.StartNode)));
Debug.WriteLine("Removed unconnected nodes:");
Debug.WriteLine(" removed nodes: " + (nodeCountBefore - _nodeStates.SearchSpaceSize));
// Even the basic degree reductions hurt the AdvancedSolver's performance.
// Reenabling should be tested when other algorithm parts are changed/improved.
// todo experiment with reductions and AdvancedSolver
if (_nodeStates.VariableTargetNodeCount > 0)
{
return(CreateResult());
}
// Initialize node states and edges. Edges are calculated from the information in the
// GraphNode. Adjacency information from GraphNode instances must not be used after this.
_data.EdgeSet = ComputeEdges();
var initialNodeCount = _nodeStates.SearchSpaceSize;
var initialEdgeCount = _data.EdgeSet.Count;
Debug.WriteLine("Initial counts:\n"
+ " nodes: " + initialNodeCount + "\n"
+ " non targets: " + (_nodeStates.SearchSpaceSize - _nodeStates.TargetNodeCount) + "\n"
+ " variable targets: " + _nodeStates.VariableTargetNodeCount + "\n"
+ " fixed targets: " + _nodeStates.FixedTargetNodeCount + "\n"
+ " edges: " + initialEdgeCount);
// Execute an initial DegreeTest.
var degreeTest = new DegreeTest(_nodeStates, _data);
var dummy = 0;
degreeTest.RunTest(ref dummy, ref dummy);
// Update _searchSpace, _edgeSet and _distanceLookup
ContractSearchSpace();//Potential bug here as Cache size decreases if distance indices not updated
// These values may become lower by merging nodes. Since the reductions based on these distance
// don't help if there are many variable target nodes, it is not really worth it to always recalculate them.
// It would either slow the preprocessing by like 30% or would need an approximation algorithm.
_data.SMatrix = new BottleneckSteinerDistanceCalculator(distanceLookup.DistanceLookup)
.CalcBottleneckSteinerDistances(_nodeStates.FixedTargetNodeIndices);
// The set of reduction test that are run until they are no longer able to reduce the search space.
var tests = new List <SteinerReduction>
{
new FarAwayNonTerminalsTest(_nodeStates, _data),
new PathsWithManyTerminalsTest(_nodeStates, _data),
new NonTerminalsOfDegreeKTest(_nodeStates, _data),
new NearestVertexTest(_nodeStates, _data)
};
// Run every reduction test (each followed by a simple degree reduction test) until they are no longer able
// to reduce the search space or 10 reduction rounds were executed.
// (the 10 round limit is never actually reached from what I've seen)
for (int i = 1; i < 11; ++i)
{
var edgeElims = 0;
var nodeElims = 0;
foreach (var test in tests.Where(t => t.IsEnabled))
{
if (!test.RunTest(ref edgeElims, ref nodeElims))
{
test.IsEnabled = false;
}
degreeTest.RunTest(ref edgeElims, ref nodeElims);
}
Debug.WriteLine("Eliminations in round {0}:", i);
Debug.WriteLine(" removed nodes: " + nodeElims);
Debug.WriteLine(" removed edges: " + edgeElims);
// No test should be still enabled in this case so we can stop running them.
if (edgeElims == 0)
{
break;
}
}
// Calculate the final search space.
ContractSearchSpace();
Debug.WriteLine("Final counts:\n"
+ " nodes: " + _nodeStates.SearchSpaceSize + " (of " + initialNodeCount + " after basic reductions)\n"
+ " non targets: " + (_nodeStates.SearchSpaceSize - _nodeStates.TargetNodeCount) + "\n"
+ " variable targets: " + _nodeStates.VariableTargetNodeCount + "\n"
+ " fixed targets: " + _nodeStates.FixedTargetNodeCount + "\n"
+ " edges: " + _data.EdgeSet.Count + " (of " + initialEdgeCount + " after basic reductions)");
return(CreateResult());
}
