135 lines
4.4 KiB
C++
135 lines
4.4 KiB
C++
// Copyright 2010-2017 Google
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef OR_TOOLS_LP_DATA_SPARSE_COLUMN_H_
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#define OR_TOOLS_LP_DATA_SPARSE_COLUMN_H_
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#include "ortools/lp_data/sparse_vector.h"
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namespace operations_research {
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namespace glop {
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// TODO(user): Consider using kInvalidRow for this?
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const RowIndex kNonPivotal(-1);
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// Specialization of SparseVectorEntry and SparseColumnIterator for the
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// SparseColumn class. In addtion to index(), it also provides row() for better
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// readability on the client side.
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class SparseColumnEntry : public SparseVectorEntry<RowIndex> {
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public:
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// Returns the row of the current entry.
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RowIndex row() const { return index(); }
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protected:
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SparseColumnEntry(const RowIndex* indices, const Fractional* coefficients,
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EntryIndex i)
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: SparseVectorEntry<RowIndex>(indices, coefficients, i) {}
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};
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using SparseColumnIterator = SparseVectorIterator<SparseColumnEntry>;
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// A SparseColumn is a SparseVector<RowIndex>, with a few methods renamed
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// to help readability on the client side.
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class SparseColumn : public SparseVector<RowIndex, SparseColumnIterator> {
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public:
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SparseColumn() : SparseVector<RowIndex, SparseColumnIterator>() {}
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// Use a separate API to get the row and coefficient of entry #i.
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RowIndex EntryRow(EntryIndex i) const { return GetIndex(i); }
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Fractional EntryCoefficient(EntryIndex i) const { return GetCoefficient(i); }
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RowIndex GetFirstRow() const { return GetFirstIndex(); }
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RowIndex GetLastRow() const { return GetLastIndex(); }
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void ApplyRowPermutation(const RowPermutation& p) {
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ApplyIndexPermutation(p);
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}
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void ApplyPartialRowPermutation(const RowPermutation& p) {
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ApplyPartialIndexPermutation(p);
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}
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};
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// --------------------------------------------------------
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// RandomAccessSparseColumn
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// --------------------------------------------------------
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// A RandomAccessSparseColumn is a mix between a DenseColumn and a SparseColumn.
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// It makes it possible to populate a dense column from a sparse column in
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// O(num_entries) instead of O(num_rows), and to access an entry in O(1).
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// As the constructor runs in O(num_rows), a RandomAccessSparseColumn should be
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// used several times to amortize the creation cost.
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class RandomAccessSparseColumn {
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public:
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// Creates a RandomAccessSparseColumn.
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// Runs in O(num_rows).
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explicit RandomAccessSparseColumn(RowIndex num_rows);
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virtual ~RandomAccessSparseColumn();
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// Clears the column.
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// Runs in O(num_entries).
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void Clear();
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void Resize(RowIndex num_rows);
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// Sets value at row.
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// Runs in O(1).
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void SetCoefficient(RowIndex row, Fractional value) {
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column_[row] = value;
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MarkRowAsChanged(row);
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}
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// Adds value to the current value at row.
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// Runs in O(1).
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void AddToCoefficient(RowIndex row, Fractional value) {
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column_[row] += value;
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MarkRowAsChanged(row);
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}
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// Populates from a sparse column.
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// Runs in O(num_entries).
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void PopulateFromSparseColumn(const SparseColumn& sparse_column);
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// Populates a sparse column from the lazy dense column.
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// Runs in O(num_entries).
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void PopulateSparseColumn(SparseColumn* sparse_column) const;
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// Returns the number of rows.
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// Runs in O(1).
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RowIndex GetNumberOfRows() const { return RowIndex(column_.size()); }
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// Returns the value in position row.
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// Runs in O(1).
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Fractional GetCoefficient(RowIndex row) const { return column_[row]; }
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private:
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// Keeps a trace of which rows have been changed.
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void MarkRowAsChanged(RowIndex row) {
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if (!changed_[row]) {
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changed_[row] = true;
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row_change_.push_back(row);
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}
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}
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// The dense version of the column.
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DenseColumn column_;
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// Dense Boolean vector used to mark changes.
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DenseBooleanColumn changed_;
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// Stack to store changes.
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std::vector<RowIndex> row_change_;
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DISALLOW_COPY_AND_ASSIGN(RandomAccessSparseColumn);
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};
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} // namespace glop
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} // namespace operations_research
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#endif // OR_TOOLS_LP_DATA_SPARSE_COLUMN_H_
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