fix random generator capacity, add Dinic's algo, add options for filtering empty flows & displaying residual graph

src/algorithms/dinic.rs

@@ -0,0 +1,107 @@
+// Dinic
+use std::cmp::min;
+use std::collections::VecDeque;
+
+use petgraph::{stable_graph::{EdgeReference, NodeIndex, StableGraph}, visit::{EdgeRef, VisitMap, Visitable}, Direction};
+
+fn available_capacity(edge: (u64, u64)) -> u64 {
+    edge.1 - edge.0
+}
+
+// BFS
+fn layer_graph(graph: StableGraph<(f32, f32), (u64, u64)>, source: NodeIndex, destination: NodeIndex) -> StableGraph<(f32, f32), (u64, u64)> {
+    // filter graph for edges with no remaining capacity
+    let mut layer_graph = graph.filter_map(|_, n| {
+        Some(*n)
+    }, |_, &e| {
+        match available_capacity(e) {
+            0 => None,
+            _ => Some(e),
+        }
+    });
+
+    // filter graph for s-t paths
+    let mut visited = layer_graph.visit_map();
+    let mut queue = VecDeque::from([(source, 0)]);
+    while let Some((node, layer)) = queue.pop_front() {
+        //let outgoing_edges = layer_graph.edges_directed(node, Direction::Outgoing).collect::<Vec<_>>();
+        let outgoing_edges = layer_graph.edges_directed(node, Direction::Outgoing).map(|e| e.id()).collect::<Vec<_>>();
+        visited.visit(node);
+
+        for edge in outgoing_edges {
+            let neighbor = layer_graph.edge_endpoints(edge).expect("edge index not found").1;
+            // if neighbor is unvisited, this is the shortest path to neighbor -> keep the edge
+            if !visited.is_visited(&neighbor) {
+                visited.visit(neighbor);
+                // stop traversing this path if destination is reached
+                if neighbor == destination {
+                    continue;
+                } else {
+                    // add neighbor to queue if destination is not reached
+                    queue.push_back((neighbor, layer+1));
+                }
+            } else {
+                // if neighbor was visited before this edge is not on the shortest path -> remove it
+                layer_graph.remove_edge(edge);
+            }
+        }
+    }
+
+    layer_graph
+}
+
+// Runs a depth Depth First Search (DFS) which returns an augmenting path from source to destination if possible
+fn dfs(graph: &StableGraph<(f32, f32), (u64, u64)>, source: NodeIndex, destination: NodeIndex) -> Option<Vec<NodeIndex>> {
+    let mut visited = graph.visit_map();
+    let mut stack = VecDeque::from([(source, vec![source])]);
+
+    // work through the main stack
+    while let Some((node, path)) = stack.pop_front() {
+        let outgoing_edges = graph.edges_directed(node, Direction::Outgoing);
+        visited.visit(node);
+
+        // iterate over all outgoing edges & add neighboring nodes to the stack
+        for edge in outgoing_edges {
+            let neighbor = edge.target();
+            if !visited.is_visited(&neighbor) && available_capacity(*edge.weight()) > 0 {
+                visited.visit(neighbor);
+                let mut new_path = path.clone();
+                new_path.push(neighbor);
+                // TODO: is this right?
+                if neighbor == destination {
+                    return Some(new_path);
+                } else {
+                    stack.push_front((neighbor, new_path));
+                }
+            };
+        }
+    }
+
+    None
+}
+
+pub fn dinic(graph: StableGraph<(f32, f32), (u64, u64)>, source: NodeIndex, sink: NodeIndex) -> StableGraph<(f32, f32), (u64, u64)> {
+    // construct layer graph (from s to t)
+    let mut g_l = layer_graph(graph, source, sink);
+
+    // construct a blocking flow in the layer graph using a DFS
+    // continue while there are augmenting paths
+    while let Some(path) = dfs(&g_l, source, sink)  {
+        // find all edges along the path
+        let edges: Vec<petgraph::prelude::EdgeIndex> = path.windows(2).map(|w| g_l.find_edge(w[0], w[1]).expect("edge not found")).collect();
+        // find bottleneck capacity along path
+        let increase_value = edges.iter().fold(u64::MAX, |m, x| {
+            let edge = g_l.edge_weight(*x).expect("edge index not found");
+            min(m, edge.1 - edge.0)
+        });
+
+        // increase flow with bottleneck capacity along the augmenting path
+        for edge in edges {
+            let weight = g_l.edge_weight_mut(edge).expect("edge not found");
+            (*weight).0 += increase_value;
+        }
+    }
+
+    // add blocking flow to flow of original graph
+    g_l
+}

src/algorithms/mod.rs

@@ -1,5 +1,7 @@
 mod edmonds_karp;
 mod ford_fulkerson;
+mod dinic;
 
 pub use ford_fulkerson::ford_fulkerson;
-pub use edmonds_karp::edmonds_karp;
+pub use edmonds_karp::edmonds_karp;
+pub use dinic::dinic;

src/main.rs

@@ -7,26 +7,51 @@ use std::{fmt::Display, ptr::fn_addr_eq};
 
 use random_generator::MaxflowProblem;
 use layout::CustomEdgeShape;
-use crate::algorithms::{ford_fulkerson, edmonds_karp};
+use crate::algorithms::{ford_fulkerson, edmonds_karp, dinic};
+use graph::{ResidualGraph, GuiGraph, FlowGraph};
 
 mod random_generator;
 mod algorithms;
 mod layout;
+mod graph;
 
 type MaxflowFn = fn(StableGraph<(f32, f32), (u64, u64)>, NodeIndex, NodeIndex) -> StableGraph<(f32, f32), (u64, u64)>;
 
 pub struct MaxflowApp {
     g: Graph<(f32, f32), (u64, u64), Directed, u32, DefaultNodeShape, CustomEdgeShape>,
     p: MaxflowProblem,
+    r: StableGraph<(f32, f32), (u64, u64)>,
     node_count: u64,
     max_capacity: u64,
     algorithm: MaxflowFn,
+    display_residual: bool,
+    display_active_flows: bool,
 }
 
 impl MaxflowApp {
     fn new(_: &CreationContext<'_>) -> Self {
         let problem = MaxflowProblem::new(10, 10);
-        Self { g: problem.to_gui_graph(), p: problem, node_count: 10, max_capacity: 5, algorithm: ford_fulkerson }
+        Self {
+            g: problem.g.to_gui_graph(problem.s, problem.t, false),
+            r: StableGraph::default(),
+            p: problem, node_count: 10,
+            max_capacity: 5,
+            algorithm: ford_fulkerson,
+            display_residual: false,
+            display_active_flows: false,
+        }
+    }
+
+    fn update_graph(&mut self) {
+        let mut graph = match self.display_residual {
+            true => &self.p.g.residual(),
+            false => &self.p.g,
+        };
+        if self.display_active_flows {
+            self.g = graph.filter_empty_flows().to_gui_graph(self.p.s, self.p.t, self.display_active_flows);
+        } else {
+            self.g = graph.to_gui_graph(self.p.s, self.p.t, self.display_active_flows);
+        }
     }
 }
 
@@ -50,7 +75,7 @@ impl App for MaxflowApp {
                             // TODO: add generation strategy (random, pseudo-random)
                             if ui.button("generate graph").clicked() {
                                 self.p = random_generator::MaxflowProblem::new(self.node_count, self.max_capacity);
-                                self.g = self.p.to_gui_graph();
+                                self.update_graph();
                             }
                         });
 
@@ -61,20 +86,36 @@ impl App for MaxflowApp {
                                 .selected_text(format!("{}", match self.algorithm {
                                     _ if fn_addr_eq(self.algorithm, ford_fulkerson as MaxflowFn) => "Ford-Fulkerson",
                                     _ if fn_addr_eq(self.algorithm, edmonds_karp as MaxflowFn) => "Edmonds-Karp",
+                                    _ if fn_addr_eq(self.algorithm, dinic as MaxflowFn) => "Dinic",
                                     _ => "unknown"
                                 }))
                                 .show_ui(ui, |ui| {
                                     ui.selectable_value(&mut self.algorithm, ford_fulkerson, "Ford-Fulkerson");
                                     ui.selectable_value(&mut self.algorithm, edmonds_karp, "Edmonds-Karp");
+                                    ui.selectable_value(&mut self.algorithm, dinic, "Dinic");
                                 });
                             if ui.button("run algorithm").clicked() {
                                 let max_flow_graph = ford_fulkerson(self.p.g.clone(), self.p.s, self.p.t);
                                 self.p = MaxflowProblem::from(max_flow_graph, self.p.s, self.p.t);
-                                self.g = self.p.to_gui_graph();
+                                self.update_graph();
+                            }
+                            if ui.button("reset").clicked() {
+                                self.p.reset_flow();
+                                self.update_graph();
                             }
-                            // reset button
                             // step button (disable when finished)
                         });
+
+                    CollapsingHeader::new("Display options")
+                        .default_open(true)
+                        .show(ui, |ui| {
+                            if ui.checkbox(&mut self.display_residual, "show residual graph").changed() {
+                                self.update_graph();
+                            }
+                            if ui.checkbox(&mut self.display_active_flows, "show active flows only").changed() {
+                                self.update_graph();
+                            }
+                        })
                 });
 
 

src/random_generator.rs

@@ -1,3 +1,4 @@
+use petgraph::data::Build;
 use petgraph::stable_graph::{StableGraph, NodeIndex};
 use petgraph::{Directed};
 use egui_graphs::{default_edge_transform, default_node_transform, to_graph_custom, DefaultEdgeShape, DefaultNodeShape, Graph};
@@ -70,9 +71,10 @@ impl MaxflowProblem {
                 // otherwise insert the edge and its residual edge
                 inserted_edges.push((node1, node2));
                 inserted_edges.push((node2, node1));
-                let capacity: u64 = rng.gen_range(1..=max_capacity);
-                graph.add_edge(node1, node2, (0, capacity));
-                graph.add_edge(node2, node1, (0, capacity));
+                let capacity1: u64 = rng.gen_range(1..=max_capacity);
+                let capacity2: u64 = rng.gen_range(1..=max_capacity);
+                graph.add_edge(node1, node2, (0, capacity1));
+                graph.add_edge(node2, node1, (0, capacity2));
             }
         }
 
@@ -101,6 +103,14 @@ impl MaxflowProblem {
         }
     }
 
+    // set all flows back to zero
+    pub fn reset_flow(&mut self) {
+        for edge in self.g.edge_indices().collect::<Vec<_>>() {
+            let weight = self.g.edge_weight_mut(edge).expect("edge not found");
+            (*weight).0 = 0;
+        }
+    }
+
     pub fn to_gui_graph(&self) -> Graph<(f32, f32), (u64, u64), Directed, u32, DefaultNodeShape, CustomEdgeShape> {
         let mut graph = to_graph_custom(&self.g,
             |n| {