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flow_problem.proto
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flow_problem.proto
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// Copyright 2010-2018 Google LLC
// 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.
// Protobuf representing a flow problem on a graph. It supports several problem
// types. Depending on the type, the message is interpreted differently as
// explained under each type description below.
//
// LINEAR_SUM_ASSIGNMENT: the algorithm computes the minimum-cost perfect
// matching if there is one.
// - Arcs are assumed to be from a left node to a right node. In particular
// the id space of the left and right nodes can be the same. That is an arc
// from the left node 0 to the right node 0 will be coded as (0, 0).
// - If a perfect matching does not exist, the problem is not feasible.
// - Capacity and supply values are ignored.
//
// MAX_FLOW: The algorithm computes the maximum flow under the arc capacity
// constraints.
// - Only one source (with supply > 0) and one sink (with supply < 0), the
// supply values are not important. Only the signs are.
// - The costs are ignored.
//
// MIN_COST_FLOW: the algorithm computes the flow of minimum cost. If a feasible
// flow does not exist (in particular if the sum of supplies is not 0), the
// problem is not feasible.
syntax = "proto2";
package operations_research;
message Arc {
// A directed arc goes from a tail node to a head node.
// Node ids must be non-negative (>= 0).
optional int64 tail_node_id = 1;
optional int64 head_node_id = 2;
// Capacity of the arc. Must be non-negative (>= 0). If the capacity is zero,
// it is equivalent to not including the arc in the FlowModel.
optional int64 capacity = 3 [default = 1];
// Cost of this arc per unit of flow.
// Note that it can take any positive, negative or null value.
optional int64 unit_cost = 4 [default = 0];
}
message Node {
// The ids must be non-negative (>= 0). They should be dense for good
// performance. Note that it is not mandatory to include nodes with no supply
// in a FlowModel.
optional int64 id = 1;
// The supply can be positive or negative in which case it means demand.
// The sum of the supplies over all nodes must always be 0.
optional int64 supply = 2 [default = 0];
}
// Holds a flow problem, see Node and Arc for more details.
message FlowModel {
repeated Node node = 1;
repeated Arc arc = 2;
// The type of problem to solve.
enum ProblemType {
LINEAR_SUM_ASSIGNMENT = 0;
MAX_FLOW = 1;
MIN_COST_FLOW = 2;
}
optional ProblemType problem_type = 3 [default = MIN_COST_FLOW];
}