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/*
* Copyright 2008-2009 NVIDIA Corporation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <cusp/array1d.h>
namespace cusp
{
namespace graph
{
namespace detail
{
namespace host
{
template <typename Matrix, typename IndexType>
void propagate_distances(const Matrix& A,
const IndexType i,
const size_t d,
const size_t k,
cusp::array1d<size_t,cusp::host_memory>& distance)
{
distance[i] = d;
if (d < k)
{
for(IndexType jj = A.row_offsets[i]; jj < A.row_offsets[i + 1]; jj++)
{
IndexType j = A.column_indices[jj];
// update only if necessary
if (d + 1 < distance[j])
propagate_distances(A, j, d + 1, k, distance);
}
}
}
////////////////
// Host Paths //
////////////////
template <typename Matrix, typename Array>
size_t maximal_independent_set(const Matrix& A, Array& stencil, size_t k)
{
typedef typename Matrix::index_type IndexType;
const IndexType N = A.num_rows;
// distance to nearest MIS node
cusp::array1d<size_t,cusp::host_memory> distance(N, k + 1);
// count number of MIS nodes
size_t set_nodes = 0;
// pick MIS-k nodes greedily and deactivate all their k-neighbors
for(IndexType i = 0; i < N; i++)
{
if (distance[i] > k)
{
set_nodes++;
// reset distances on all k-ring neighbors
propagate_distances(A, i, 0, k, distance);
}
}
// write output
stencil.resize(N);
for (IndexType i = 0; i < N; i++)
stencil[i] = distance[i] == 0;
return set_nodes;
}
} // end namespace host
} // end namespace detail
} // end namespace graph
} // end namespace cusp
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