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askrene algorithm add helper for flow conservation

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Changelog-None: askrene algorithm add helper for flow conservation

Signed-off-by: Lagrang3 <lagrang3@protonmail.com>
This commit is contained in:
Lagrang3
2024-10-17 11:28:57 +01:00
committed by Rusty Russell
parent 42d075cc97
commit 1dfa562cd9
1 changed files with 30 additions and 11 deletions
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41
plugins/askrene/algorithm.c
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@@ -212,11 +212,35 @@ static s64 get_augmenting_flow(const struct graph *graph,
return flow;
}
/* Helper.
* Sends an amount of flow through an arc, changing the flow balance of the
* nodes connected by the arc and the [residual] capacity of the arc and its
* dual. */
static inline void sendflow(const struct graph *graph, const struct arc arc,
const s64 flow, s64 *arc_capacity,
s64 *node_balance)
{
const struct arc dual = arc_dual(graph, arc);
arc_capacity[arc.idx] -= flow;
arc_capacity[dual.idx] += flow;
if (node_balance) {
const struct node src = arc_tail(graph, arc),
dst = arc_tail(graph, dual);
node_balance[src.idx] -= flow;
node_balance[dst.idx] += flow;
}
}
/* Augment a `flow` amount along the path defined by `prev`.*/
static void augment_flow(const struct graph *graph,
const struct node source,
const struct node target,
const struct arc *prev,
s64 *excess,
s64 *capacity,
s64 flow)
{
@@ -232,15 +256,8 @@ static void augment_flow(const struct graph *graph,
while (cur.idx != source.idx) {
assert(cur.idx < max_num_nodes);
const struct arc arc = prev[cur.idx];
const struct arc dual = arc_dual(graph, arc);
assert(arc.idx < max_num_arcs);
assert(dual.idx < max_num_arcs);
capacity[arc.idx] -= flow;
capacity[dual.idx] += flow;
assert(capacity[arc.idx] >= 0);
sendflow(graph, arc, flow, capacity, excess);
/* we are traversing in the opposite direction to the flow,
* hence the next node is at the tail of the arc. */
@@ -249,7 +266,7 @@ static void augment_flow(const struct graph *graph,
/* We may never have a path exceeds the number of nodes, it this
* happens it means we have an infinite loop. */
path_length++;
if(path_length >= max_num_nodes)
if (path_length >= max_num_nodes)
break;
}
assert(path_length < max_num_nodes);
@@ -297,7 +314,8 @@ bool simple_feasibleflow(const tal_t *ctx,
delta = MIN(amount, delta);
assert(delta > 0 && delta <= amount);
augment_flow(graph, source, destination, prev, capacity, delta);
augment_flow(graph, source, destination, prev, NULL, capacity,
delta);
amount -= delta;
}
finish:
@@ -368,7 +386,8 @@ bool simple_mcf(const tal_t *ctx, const struct graph *graph,
delta = MIN(remaining_amount, delta);
assert(delta > 0 && delta <= remaining_amount);
augment_flow(graph, source, destination, prev, capacity, delta);
augment_flow(graph, source, destination, prev, NULL, capacity,
delta);
remaining_amount -= delta;
/* update potentials */