Java Reference

Java Reference

LinearExprBuilder.java
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1// Copyright 2010-2021 Google LLC
2// Licensed under the Apache License, Version 2.0 (the "License");
3// you may not use this file except in compliance with the License.
4// You may obtain a copy of the License at
5//
6// http://www.apache.org/licenses/LICENSE-2.0
7//
8// Unless required by applicable law or agreed to in writing, software
9// distributed under the License is distributed on an "AS IS" BASIS,
10// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
11// See the License for the specific language governing permissions and
12// limitations under the License.
13
14package com.google.ortools.sat;
15
16import java.util.Map;
17import java.util.TreeMap;
18
20public final class LinearExprBuilder implements LinearArgument {
21 private final TreeMap<Integer, Long> coefficients;
22 private long offset;
23
25 this.coefficients = new TreeMap<>();
26 this.offset = 0;
27 }
28
30 addTerm(expr, 1);
31 return this;
32 }
33
34 public LinearExprBuilder add(long constant) {
35 offset = offset + constant;
36 return this;
37 }
38
39 public LinearExprBuilder addTerm(LinearArgument expr, long coeff) {
40 final LinearExpr e = expr.build();
41 final int numElements = e.numElements();
42 for (int i = 0; i < numElements; ++i) {
43 coefficients.merge(e.getVariableIndex(i), e.getCoefficient(i) * coeff, Long::sum);
44 }
45 offset = offset + e.getOffset() * coeff;
46 return this;
47 }
48
50 for (final LinearArgument expr : exprs) {
51 addTerm(expr, 1);
52 }
53 return this;
54 }
55
56 public LinearExprBuilder addWeightedSum(LinearArgument[] exprs, long[] coeffs) {
57 for (int i = 0; i < exprs.length; ++i) {
58 addTerm(exprs[i], coeffs[i]);
59 }
60 return this;
61 }
62
63 public LinearExprBuilder addWeightedSum(LinearArgument[] exprs, int[] coeffs) {
64 for (int i = 0; i < exprs.length; ++i) {
65 addTerm(exprs[i], coeffs[i]);
66 }
67 return this;
68 }
69
70 @Override
71 public LinearExpr build() {
72 int numElements = 0;
73 int lastVarIndex = -1;
74 long lastCoeff = 0;
75 for (Map.Entry<Integer, Long> entry : coefficients.entrySet()) {
76 if (entry.getValue() != 0) {
77 numElements++;
78 lastVarIndex = entry.getKey();
79 lastCoeff = entry.getValue();
80 }
81 }
82 if (numElements == 0) {
83 return new ConstantExpression(offset);
84 } else if (numElements == 1) {
85 return new AffineExpression(lastVarIndex, lastCoeff, offset);
86 } else {
87 int[] varIndices = new int[numElements];
88 long[] coeffs = new long[numElements];
89 int index = 0;
90 for (Map.Entry<Integer, Long> entry : coefficients.entrySet()) {
91 if (entry.getValue() != 0) {
92 varIndices[index] = entry.getKey();
93 coeffs[index] = entry.getValue();
94 index++;
95 }
96 }
97 return new WeightedSumExpression(varIndices, coeffs, offset);
98 }
99 }
100}
A specialized linear expression: a * x + b.
A specialized constant linear expression.
Builder class for the LinearExpr container.
LinearExprBuilder addWeightedSum(LinearArgument[] exprs, int[] coeffs)
LinearExprBuilder addSum(LinearArgument[] exprs)
LinearExprBuilder add(LinearArgument expr)
LinearExpr build()
Builds a linear expression.
LinearExprBuilder addWeightedSum(LinearArgument[] exprs, long[] coeffs)
LinearExprBuilder add(long constant)
LinearExprBuilder addTerm(LinearArgument expr, long coeff)
A specialized linear expression: sum(ai * xi) + b.
A object that can build a LinearExpr object.
LinearExpr build()
Builds a linear expression.
A linear expression (sum (ai * xi) + b).
Definition: LinearExpr.java:19
long getCoefficient(int index)
Returns the ith coefficient.
int numElements()
Returns the number of terms (excluding the constant one) in this expression.
long getOffset()
Returns the constant part of the expression.
int getVariableIndex(int index)
Returns the index of the ith variable.