Function max_flow_value 

pub fn max_flow_value(
    graph: &Graph,
    source: VertexId,
    target: VertexId,
    capacity: Option<&[f64]>,
) -> IgraphResult<f64>

Scalar maximum-flow value from source to target.

Counterpart of igraph_maxflow_value in references/igraph/src/flow/flow.c (igraph C uses Goldberg-Tarjan push-relabel; this implementation uses Dinic’s algorithm — the scalar value matches by the max-flow / min-cut uniqueness theorem).

Arguments

• graph — input graph (directed or undirected).
• source — source vertex id (0 ≤ source < vcount()).
• target — sink vertex id (0 ≤ target < vcount(), target != source).
• capacity — optional per-edge capacity in the graph’s edge-id order. When None, each edge contributes unit capacity. When Some(c), c.len() must equal graph.ecount(), and every entry must be finite and ≥ 0.

Returns

The maximum total flow value as f64, summing to 0.0 when source and target are in disjoint connected components or when every source → target path is blocked by zero-capacity edges.

Errors

• IgraphError::VertexOutOfRange if source or target is outside [0, vcount()).
• IgraphError::InvalidArgument if source == target, the capacity slice length differs from ecount(), or any capacity is negative / non-finite.

Examples

use rust_igraph::{Graph, max_flow_value};

// Two parallel paths of capacity 1 each → max flow = 2.
let mut g = Graph::new(4, true).unwrap();
g.add_edge(0, 1).unwrap();
g.add_edge(1, 3).unwrap();
g.add_edge(0, 2).unwrap();
g.add_edge(2, 3).unwrap();
let cap = vec![1.0, 1.0, 1.0, 1.0];
let f = max_flow_value(&g, 0, 3, Some(&cap)).unwrap();
assert!((f - 2.0).abs() < 1e-12);