checkpoint 2025-08-22

README.md

@@ -7,36 +7,36 @@
 - Create a custom to_graph method which displays a maxflow graph
 
 TODOs
-- [ ] Implementation of Algos:
+- [x] Implementation of Algos:
     - [x] Ford-Fulkersson (DFS zur Berechnung des flusserhöhenden/augmentierenden Pfads)
     - [x] Edmonds-Karp (BFS zur Berechnung des flusserhöhenden/augmnetierenden Pfads)
     - [x] Dinic
-    - [ ] Goldberg-Tarjan/Preflow-Push
+    - [x] Goldberg-Tarjan/Preflow-Push
-- [ ] Step-by-step implementation for all algos
+- [x] Step-by-step implementation for all algos
     - [x] Ford-Fulkerson
     - [x] Edmonds-Karp
     - [x] Dinic
-    - [ ] Goldberg-Tarjan/Preflow-Push
+    - [x] Goldberg-Tarjan/Preflow-Push
 - [x] Mark edges which have active flows with a color
 - [x] Move GUI Graph conversion to a trait of StableGraph
-- [ ] Add graph positioning strategy which looks "nicer"#
+- [ ] Add graph positioning strategy which looks "nicer"
     - [x] Only insert nodes which are at least a distance of 40 away (default)
     - [ ] Pseudo-random node positioning strategy
-- [ ] Handle residual edges properly
+- [x] Handle residual edges properly
     - [x] Add display option for residual edges
 - [x] Only show active flows (filter all edges with f=0)
-- [ ] Show normal vs residual graph
+- [x] Show normal vs residual graph -> not needed, residual graph is shown by default
 - [x] When increasing flows, handle residual path
-- [ ] Add unit tests
+- [x] Add unit tests
-    - [ ] With small problems to prove correctness
+    - [x] With small problems to prove correctness
-    - [ ] For Benchmarking the algos
+    - [x] For Benchmarking the algos
-    - [ ] Check validity of the generated flows (incoming flows = outgoing flows; flow <= capacity)
+    - [x] Check validity of the generated flows (incoming flows = outgoing flows; flow <= capacity)
-- [ ] Add info display pane
+- [x] Add info display pane
     - [x] is valid flow? (add trait to graph)
     - [x] current total flow (add trait to calculate)
-    - [ ] number of steps
+    - [x] number of steps (is implemented for stepwise)
-- [ ] implement PartialEq for StableGraph (not really possible -> how do you compare graphs?)
+- [x] implement PartialEq for StableGraph (not really possible -> how do you compare graphs?) -> implemented a prune_zero trait & compare node/edge weights for same index
-- [ ] Step-by-step vizualisation with choosable time delay
+- [x] Step-by-step vizualisation with choosable time delay
 - [ ] Dinic: add GUI options to show Layer Graph and Blocking flow
 - [ ] Goldberg-Tarjan: show distance labels at nodes
 - [x] change GUI colors to accomodate color-blindness (blue-yellow rather than red-green)

src/algorithms/goldberg_tarjan.rs

@@ -97,13 +97,11 @@ impl MaxflowAlgorithm for GoldbergTarjan {
         // if the distance labels were not already computed, compute them now
         if self.distance_label == None {
             self.compute_distances();
-            //println!("distance labeling: {:?}", self.distance_label);
         }
         
         // Main loop: while there is an active node, continue
         if let Some((node, excess)) = self.active_node() {
             // find all outgoing edges with available capacity
-            //println!("active node {:?} source {:?} sink {:?}", node, self.source, self.sink);
             let valid_edges: Vec<petgraph::prelude::EdgeIndex> = self.residual_graph
                 .edges_directed(node, Direction::Outgoing)
                 .filter(|e| (e.weight().1 - e.weight().0) > 0 )
@@ -112,20 +110,11 @@ impl MaxflowAlgorithm for GoldbergTarjan {
                 .collect::<Vec<_>>();
             if valid_edges.len() > 0 {
                 // node has valid edges -> push (move min[excess, capacity] to first valid edge)
-                //println!("push");
                 let edge = valid_edges[0];
-                // let (source, target) = self.residual_graph.edge_endpoints(edge).expect("edge not connected");
                 let available_capacity = self.residual_graph.edge_weight(edge).expect("Invalid edge index").1 - self.residual_graph.edge_weight(edge).expect("Invalid edge index").0;
                 let additional_flow = min(excess, available_capacity);
                 self.residual_graph.add_flow(edge, additional_flow);
                 
-                // // increase flow of the forward edge with the calculated bottleneck value
-                // let weight: &mut (u64, u64) = self.residual_graph.edge_weight_mut(edge).expect("edge not found");
-                // (*weight).0 += additional_flow;
-                // // increase capacity of the residual edge of the with the calculated bottleneck value
-                // let residual_edge = self.residual_graph.find_edge(target, source).expect("residual edge not found");
-                // let residual_weight: &mut (u64, u64) = self.residual_graph.edge_weight_mut(residual_edge).expect("edge not found");
-                // (*residual_weight).1 += additional_flow;
             } else {
                 // node has no valid edges -> relabel (increase node distance label to min[neighbors] + 1)
                 let neighbors = self.residual_graph
@@ -134,8 +123,8 @@ impl MaxflowAlgorithm for GoldbergTarjan {
                     .sorted_by_key(|e| self.distance_label.as_ref().expect("distance labelling not present").get(&e.target()))
                     .map(|e| e.target())
                     .collect::<Vec<_>>();
+                assert!(neighbors.len() > 0);
                 let lowest_distance = self.distance_label.as_ref().expect("distance labelling not present").get(&neighbors[0]).expect("No distance label found").clone();
-                //println!("relabel {} + 1 (index: {:?})", lowest_distance, node);
                 self.distance_label.as_mut().expect("distance labelling not present").insert(node, lowest_distance + 1);
             }
             false

src/graph.rs

@@ -76,6 +76,8 @@ pub trait FlowGraph {
 
     fn reset_flow(&mut self);
 
+    fn prune_zero(&self) -> StableGraph<(f32, f32), (u64, u64)>;
+
     fn valid_flow(&self, source: NodeIndex, sink: NodeIndex) -> bool;
     
     fn saturated_cut(&self, source: NodeIndex, sink: NodeIndex) -> bool;
@@ -153,6 +155,19 @@ impl FlowGraph for StableGraph<(f32, f32), (u64, u64)> {
         }
     }
 
+    // removes all edges where the current flow is zero & returns a pruned graph
+    fn prune_zero(&self) -> StableGraph<(f32, f32), (u64, u64)> {
+        let mut zero_graph = self.clone();
+        for edge in zero_graph.edge_indices().collect::<Vec<_>>() {
+            let weight = zero_graph.edge_weight(edge).expect("edge not found");
+            if weight.0 == 0 {
+                zero_graph.remove_edge(edge);
+            }
+        }
+
+        zero_graph
+    }
+
     // check if flow is valid:
     // - for every edge, the flow doesn't exceed the capacity
     // - for every node, the amount of incoming flows is equal to the amount of outgoing flows
@@ -199,7 +214,6 @@ impl FlowGraph for StableGraph<(f32, f32), (u64, u64)> {
         return true;
     }
 
-    // TODO: assert that incoming flows at sink are equal to outgoing flows at source (otherwise return 0)
     fn total_flow(&self, source: NodeIndex, sink: NodeIndex) -> u64 {
         let outgoing_flows_source: u64 = self.edges_directed(source, Direction::Outgoing).map(|e| e.weight().0).sum();
         let incoming_flows_source: u64 = self.edges_directed(source, Direction::Incoming).map(|e| e.weight().0).sum();
@@ -207,7 +221,9 @@ impl FlowGraph for StableGraph<(f32, f32), (u64, u64)> {
         let incoming_flows_sink: u64 = self.edges_directed(sink, Direction::Incoming).map(|e| e.weight().0).sum();
         let total_flow_source = outgoing_flows_source - incoming_flows_source;
         let total_flow_sink = incoming_flows_sink - outgoing_flows_sink;
-        assert!(total_flow_sink == total_flow_source);
+        if total_flow_sink != total_flow_source {
+            return 0;
+        }
         return total_flow_source;
     }
 
@@ -233,22 +249,38 @@ impl FlowGraph for StableGraph<(f32, f32), (u64, u64)> {
         self.edge_weight(edge).expect("edge not found").1 - self.edge_weight(edge).expect("edge not found").0
     }
     
-    fn add_flow(&mut self, edge: EdgeIndex, flow: u64) {
+    // adds the specified flow to the edge of a residual graph
-        // search for reverse edge and subtract existing flow if possible
+    fn add_flow(&mut self, forward_edge: EdgeIndex, flow: u64) {
-        let (source, target) = self.edge_endpoints(edge).expect("edge not connected");
+        // search for reverse edge
-        let residual_edge = self.find_edge(target, source).expect("residual edge not found");
+        let (source, target) = self.edge_endpoints(forward_edge).expect("edge not connected");
-        let residual_weight: &mut (u64, u64) = self.edge_weight_mut(residual_edge).expect("residual edge not found");
+        let reverse_edge = self.find_edge(target, source).expect("reverse edge not found");
-        let forward_flow = i128::from(flow) - i128::from((*residual_weight).0);
+        
-        // subtract minimum of additional_flow and residual_weight
+        // calculate how much flow needs to be added on the reverse edge
-        if residual_weight.0 > 0 {
+        let current_reverse_flow = self.edge_weight(reverse_edge).expect("reverse erge not found").0;
-            (*residual_weight).0 -= min(residual_weight.0, flow);
+        // maximum flow we can subtract from reverse edge
+        let reverse_flow = min(current_reverse_flow, flow);
+        let forward_flow = flow - reverse_flow;
+        if reverse_flow > 0 {
+            // decrease reverse flow
+            let reverse_weight: &mut (u64, u64) = self.edge_weight_mut(reverse_edge).expect("reverse edge not found");
+            (*reverse_weight).0 -= reverse_flow;
+            assert!(reverse_weight.0 <= reverse_weight.1);
+            // decrease forward capacity 
+            let forward_weight: &mut (u64, u64) = self.edge_weight_mut(forward_edge).expect("edge not found");
+            (*forward_weight).1 -= reverse_flow;
+            assert!(forward_weight.0 <= forward_weight.1);
         }
-        assert!((*residual_weight).0 <= (*residual_weight).1);
+
         // add remaining flow to forward edge
-        let forward_weight: &mut (u64, u64) = self.edge_weight_mut(edge).expect("edge not found");
         if forward_flow > 0 {
-            (*forward_weight).0 += u64::try_from(forward_flow).expect("error casting flow to u64");
+            // increase forward flow
-        }
+            let forward_weight: &mut (u64, u64) = self.edge_weight_mut(forward_edge).expect("edge not found");
-        assert!((*forward_weight).0 <= (*forward_weight).1);
+            (*forward_weight).0 += forward_flow;
+            assert!(forward_weight.0 <= forward_weight.1);
+            // increase reverse capacity
+            let reverse_weight: &mut (u64, u64) = self.edge_weight_mut(reverse_edge).expect("reverse edge not found");
+            (*reverse_weight).1 += forward_flow;
+            assert!(reverse_weight.0 <= reverse_weight.1);
+        }
     }
 }

src/main.rs

@@ -27,6 +27,7 @@ pub struct MaxflowApp {
     display_active_flows: bool,
     display_layer_graph: bool,
     algorithm_finished: bool,
+    num_steps: u64,
     test_thread: Option<JoinHandle<String>>,
     test_results: String,
     test_results_open: bool,
@@ -48,6 +49,7 @@ impl MaxflowApp {
             display_active_flows: false,
             display_layer_graph: false,
             algorithm_finished: false,
+            num_steps: 0,
             test_thread: None,
             test_results: String::default(),
             test_results_open: false,
@@ -61,6 +63,8 @@ impl MaxflowApp {
     fn reset_state(&mut self) {
         // undo finished run
         self.algorithm_finished = false;
+        // set steps to zero
+        self.num_steps = 0;
         // reinitialize the current graph from the problem
         self.current_graph = self.problem.g.clone();
         // assign new maxflow problem to the graph
@@ -120,21 +124,25 @@ impl MaxflowApp {
         match &mut self.algorithm {
             MaxflowAlgorithmEnum::FordFulkerson(x) => {
                 let finished = x.step();
+                self.num_steps += 1;
                 self.current_graph = x.graph();
                 finished
             },
             MaxflowAlgorithmEnum::EdmondsKarp(x) => {
                 let finished = x.step();
+                self.num_steps += 1;
                 self.current_graph = x.graph();
                 finished
             },
             MaxflowAlgorithmEnum::Dinic(x) => {
                 let finished = x.step();
+                self.num_steps += 1;
                 self.current_graph = x.graph();
                 finished
             },
             MaxflowAlgorithmEnum::GoldbergTarjan(x) => {
                 let finished = x.step();
+                self.num_steps += 1;
                 self.current_graph = x.graph();
                 finished
             }
@@ -234,6 +242,8 @@ impl App for MaxflowApp {
                             ui.label(format!("is valid flow: {}", self.current_graph.valid_flow(self.problem.s, self.problem.t)));
 
                             ui.label(format!("total flow: {}", self.current_graph.total_flow(self.problem.s, self.problem.t)));
+
+                            ui.label(format!("number of steps: {}", self.num_steps))
                         });
 
                     CollapsingHeader::new("Tests")

src/random_generator.rs

@@ -44,7 +44,6 @@ impl MaxflowProblem {
         // select source (s) and sink (t)
         let (s,t) = nodes.choose_multiple(&mut rng, 2).copied().collect_tuple::<(NodeIndex, NodeIndex)>().expect("not enough nodes");
 
-        // TODO: this probably takes forever...
         // iterate over all possible edges
         let mut possible_edges: Vec<(NodeIndex, NodeIndex, f32)> = Vec::new();
         for pair in nodes.clone().into_iter().combinations(2) {
@@ -141,4 +140,9 @@ impl MaxflowProblem {
             _ => false
         }
     }
+
+    fn intersects_poly(a: (f32, f32), b: (f32, f32), c: (f32, f32), d: (f32, f32)) -> bool {
+        let mut intersects = Self::intersects(a, b, c, d);
+        todo!();
+    }
 }

src/testing.rs

@@ -27,7 +27,6 @@ fn solve_problem_all_algos(problem: &MaxflowProblem) -> (f64, f64, f64, f64) {
 
     // check if all algorithms return the same total flow
     let total_flows: Vec<u64> = instances.iter_mut().map(|x| x.graph().total_flow(problem.s, problem.t)).collect();
-    println!("total flows: {:?}", total_flows);
     assert!(total_flows.iter().all(|&x| x == total_flows[0]), "algorithms return different total flows");
 
     return durations.into_iter().collect_tuple().unwrap();

tests/example_flows.rs

@@ -20,7 +20,7 @@ fn generate_small_maxflow_example() -> (StableGraph<(f32, f32), (u64, u64)>, Sta
     g.add_edge(one, two, (0,2));
     g.add_edge(two, four, (0,9));
     g.add_edge(three, t, (0,10));
-    g.add_edge(four, three, (0,6));
+    g.add_edge(four, three, (0,5)); // changed capacity to 5 to enforce a single optimal solution
     g.add_edge(four, t, (0,10));
 
     // TODO:
@@ -49,7 +49,7 @@ fn generate_small_maxflow_example() -> (StableGraph<(f32, f32), (u64, u64)>, Sta
     m.update_edge(one, two, (0,2));
     m.update_edge(two, four, (9,9));
     m.update_edge(three, t, (9,10));
-    m.update_edge(four, three, (5,6));
+    m.update_edge(four, three, (5,5)); // changed capacity to 5 to enforce a single optimal solution
     m.update_edge(four, t, (10,10));
 
     return (g, m, s, t);
@@ -57,11 +57,12 @@ fn generate_small_maxflow_example() -> (StableGraph<(f32, f32), (u64, u64)>, Sta
 
 fn graph_equal(one: StableGraph<(f32, f32), (u64, u64)>, other: StableGraph<(f32, f32), (u64, u64)>) -> bool {
     // ensure all edges have the same weights
-    println!("Graph 1: {:?}", one);
-    println!("Graph 2: {:?}", other);
     let edges = one.edge_indices().map(|e| e).collect::<Vec<_>>();
     for edge in edges {
         if one.edge_weight(edge).expect("edge index not found") != other.edge_weight(edge).expect("edge index not found") {
+            println!("Edge weights don't match");
+            println!("Graph 1: {:?}", one);
+            println!("Graph 2: {:?}", other);
             return false;
         }
     }
@@ -70,6 +71,9 @@ fn graph_equal(one: StableGraph<(f32, f32), (u64, u64)>, other: StableGraph<(f32
     let nodes = one.node_indices().map(|n| n).collect::<Vec<_>>();
     for node in nodes {
         if one.node_weight(node).expect("node index not found") != other.node_weight(node).expect("node index not found") {
+            println!("Node weights don't match");
+            println!("Graph 1: {:?}", one);
+            println!("Graph 2: {:?}", other);
             return false;
         }
     }
@@ -85,5 +89,38 @@ fn test_ford_fulkerson() {
     let mut  algo = FordFulkerson::from_problem(&problem);
     let solution = algo.run();
 
-    assert!(graph_equal(solution, m.residual()));
+    assert!(graph_equal(solution.prune_zero(), m.residual().prune_zero()));
+}
+
+#[test]
+fn test_edmonds_karp() {
+    let (g, m, s, t) = generate_small_maxflow_example();
+
+    let problem = MaxflowProblem::from(g, s, t);
+    let mut  algo = EdmondsKarp::from_problem(&problem);
+    let solution = algo.run();
+
+    assert!(graph_equal(solution.prune_zero(), m.residual().prune_zero()));
+}
+
+#[test]
+fn test_dinic() {
+    let (g, m, s, t) = generate_small_maxflow_example();
+
+    let problem = MaxflowProblem::from(g, s, t);
+    let mut  algo = Dinic::from_problem(&problem);
+    let solution = algo.run();
+
+    assert!(graph_equal(solution.prune_zero(), m.residual().prune_zero()));
+}
+
+#[test]
+fn test_goldberg_tarjan() {
+    let (g, m, s, t) = generate_small_maxflow_example();
+
+    let problem = MaxflowProblem::from(g, s, t);
+    let mut  algo = GoldbergTarjan::from_problem(&problem);
+    let solution = algo.run();
+
+    assert!(graph_equal(solution.prune_zero(), m.residual().prune_zero()));
 }