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/* ========================================================================== */
/* === Source/Mongoose_BoundaryHeap.cpp ===================================== */
/* ========================================================================== */
/* -----------------------------------------------------------------------------
* Mongoose Graph Partitioning Library Copyright (C) 2017-2018,
* Scott P. Kolodziej, Nuri S. Yeralan, Timothy A. Davis, William W. Hager
* Mongoose is licensed under Version 3 of the GNU General Public License.
* Mongoose is also available under other licenses; contact authors for details.
* -------------------------------------------------------------------------- */
#include "Mongoose_BoundaryHeap.hpp"
#include "Mongoose_CutCost.hpp"
#include "Mongoose_Debug.hpp"
#include "Mongoose_Internal.hpp"
#include "Mongoose_Logger.hpp"
namespace Mongoose
{
//-----------------------------------------------------------------------------
// This function inserts the specified vertex into the graph
//-----------------------------------------------------------------------------
void bhLoad(EdgeCutProblem *graph, const EdgeCut_Options *options)
{
/* Load the boundary heaps. */
Int n = graph->n;
Int *Gp = graph->p;
Int *Gi = graph->i;
double *Gx = graph->x;
double *Gw = graph->w;
bool *partition = graph->partition;
double *gains = graph->vertexGains;
Int *externalDegree = graph->externalDegree;
/* Keep track of the cut cost. */
CutCost cost;
cost.heuCost = 0.0;
cost.cutCost = 0.0;
cost.W[0] = 0.0;
cost.W[1] = 0.0;
cost.imbalance = 0.0;
/* Compute the gains & discover if the vertex is on the boundary. */
for (Int k = 0; k < n; k++)
{
bool kPartition = partition[k];
cost.W[kPartition] += (Gw) ? Gw[k] : 1;
double gain = 0.0;
Int exD = 0;
for (Int p = Gp[k]; p < Gp[k + 1]; p++)
{
double edgeWeight = (Gx) ? Gx[p] : 1;
bool onSameSide = (kPartition == partition[Gi[p]]);
gain += (onSameSide ? -edgeWeight : edgeWeight);
if (!onSameSide)
{
exD++;
cost.cutCost += edgeWeight;
}
}
gains[k] = gain;
externalDegree[k] = exD;
if (exD > 0)
bhInsert(graph, k);
}
/* Save the cut cost to the graph. */
graph->cutCost = cost.cutCost;
graph->W0 = cost.W[0];
graph->W1 = cost.W[1];
double targetSplit = options->target_split;
ASSERT(targetSplit > 0);
ASSERT(targetSplit <= 0.5);
graph->imbalance = targetSplit - std::min(graph->W0, graph->W1) / graph->W;
graph->heuCost = (graph->cutCost
+ (fabs(graph->imbalance) > options->soft_split_tolerance
? fabs(graph->imbalance) * graph->H
: 0.0));
}
//-----------------------------------------------------------------------------
// This function inserts the specified vertex into the graph's boundary heap
//-----------------------------------------------------------------------------
void bhInsert(EdgeCutProblem *graph, Int vertex)
{
/* Unpack structures */
Int vp = graph->partition[vertex];
Int *bhHeap = graph->bhHeap[vp];
Int size = graph->bhSize[vp];
double *gains = graph->vertexGains;
bhHeap[size] = vertex;
graph->BH_putIndex(vertex, size);
heapifyUp(graph, bhHeap, gains, vertex, size, gains[vertex]);
/* Save the size. */
graph->bhSize[vp] = size + 1;
}
//-----------------------------------------------------------------------------
// Removes the specified vertex from its heap.
// To do this, we swap the last element in the heap with the element we
// want to remove. Then we heapify up and heapify down.
//-----------------------------------------------------------------------------
void bhRemove(EdgeCutProblem *graph, const EdgeCut_Options *options, Int vertex, double gain,
bool partition, Int bhPosition)
{
(void)options; // Unused variable
(void)gain; // Unused variable
double *gains = graph->vertexGains;
Int *bhIndex = graph->bhIndex;
Int *bhHeap = graph->bhHeap[partition];
Int size = (--graph->bhSize[partition]);
/* If we removed the last position in the heap, there's nothing to do. */
if (bhPosition == size)
{
bhIndex[vertex] = 0;
return;
}
/* Replace the vertex with the last element in the heap. */
Int v = bhHeap[bhPosition] = bhHeap[size];
graph->BH_putIndex(v, bhPosition);
/* Finish the delete of "vertex" from the heap. */
bhIndex[vertex] = 0;
/* Bubble up then bubble down with a reread of v because it may have
* changed during heapifyUp. */
heapifyUp(graph, bhHeap, gains, v, bhPosition, gains[v]);
v = bhHeap[bhPosition];
heapifyDown(graph, bhHeap, size, gains, v, bhPosition, gains[v]);
}
//-----------------------------------------------------------------------------
// Starting at a position, this function will heapify from a vertex upwards
//-----------------------------------------------------------------------------
void heapifyUp(EdgeCutProblem *graph, Int *bhHeap, double *gains, Int vertex,
Int position, double gain)
{
if (position == 0)
return;
Int posParent = graph->BH_getParent(position);
Int pVertex = bhHeap[posParent];
double pGain = gains[pVertex];
/* If we need to swap this vertex with the parent then: */
if (pGain < gain)
{
bhHeap[posParent] = vertex;
bhHeap[position] = pVertex;
graph->BH_putIndex(vertex, posParent);
graph->BH_putIndex(pVertex, position);
heapifyUp(graph, bhHeap, gains, vertex, posParent, gain);
}
}
//-----------------------------------------------------------------------------
// Starting at a position, this function will heapify from a vertex downwards
//-----------------------------------------------------------------------------
void heapifyDown(EdgeCutProblem *graph, Int *bhHeap, Int size, double *gains, Int vertex,
Int position, double gain)
{
if (position >= size)
return;
Int lp = graph->BH_getLeftChild(position);
Int rp = graph->BH_getRightChild(position);
Int lv = (lp < size ? bhHeap[lp] : -1);
Int rv = (rp < size ? bhHeap[rp] : -1);
double lg = (lv >= 0 ? gains[lv] : -INFINITY);
double rg = (rv >= 0 ? gains[rv] : -INFINITY);
if (gain < lg || gain < rg)
{
if (lg > rg)
{
bhHeap[position] = lv;
graph->BH_putIndex(lv, position);
bhHeap[lp] = vertex;
graph->BH_putIndex(vertex, lp);
heapifyDown(graph, bhHeap, size, gains, vertex, lp, gain);
}
else
{
bhHeap[position] = rv;
graph->BH_putIndex(rv, position);
bhHeap[rp] = vertex;
graph->BH_putIndex(vertex, rp);
heapifyDown(graph, bhHeap, size, gains, vertex, rp, gain);
}
}
}
} // end namespace Mongoose
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