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Revert "Rewrite MinCostMaxFlow to avoid edge arrays."
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This reverts commit 357e9d0.
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@kohler
kohler committed Oct 28, 2023
1 parent 357e9d0 commit 33c6775
Showing 1 changed file with 44 additions and 63 deletions.
107 changes: 44 additions & 63 deletions lib/mincostmaxflow.php
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Original file line number Diff line number Diff line change
Expand Up @@ -25,10 +25,8 @@ class MinCostMaxFlow_Node {
public $price = 0;
/** @var int */
public $n_outgoing_admissible = 0;
/** @var ?MinCostMaxFlow_Edge */
public $e1;
/** @var ?MinCostMaxFlow_Edge */
public $epos;
/** @var list<MinCostMaxFlow_Edge> */
public $e = [];
/** @param string $name */
function __construct($name, $klass) {
$this->name = $name;
Expand All @@ -37,7 +35,7 @@ function __construct($name, $klass) {
/** @param int|float $expected
* @return void */
function check_excess($expected) {
for ($e = $this->e1; $e; $e = $e->next($this)) {
foreach ($this->e as $e) {
$expected += $e->flow_to($this);
}
if ($expected != $this->excess) {
Expand All @@ -48,7 +46,7 @@ function check_excess($expected) {
/** @return int */
function count_outgoing_price_admissible() {
$n = 0;
for ($e = $this->e1; $e; $e = $e->next($this)) {
foreach ($this->e as $e) {
if ($e->is_price_admissible_from($this))
++$n;
}
Expand All @@ -61,7 +59,7 @@ function set_price_fix_admissible($p) {
$this->price = $p;

// adjust n_outgoing_admissible counts
for ($e = $this->e1; $e; $e = $e->next($this)) {
foreach ($this->e as $e) {
$rc = $e->cost + $e->src->price - $e->dst->price;
if ($e->src === $this) {
$old_rc = $e->cost + $old_price - $e->dst->price;
Expand Down Expand Up @@ -91,10 +89,6 @@ class MinCostMaxFlow_Edge {
public $cost;
/** @var int|float */
public $flow = 0;
/** @var ?MinCostMaxFlow_Edge */
public $next_src;
/** @var ?MinCostMaxFlow_Edge */
public $next_dst;
/** @param MinCostMaxFlow_Node $src
* @param MinCostMaxFlow_Node $dst
* @param int|float $cap
Expand All @@ -107,11 +101,6 @@ function __construct($src, $dst, $cap, $cost, $mincap = 0) {
$this->mincap = $mincap;
$this->cost = $cost;
}
/** @param MinCostMaxFlow_Node $v
* @return ?MinCostMaxFlow_Edge */
function next($v) {
return $v === $this->src ? $this->next_src : $this->next_dst;
}
/** @param MinCostMaxFlow_Node $v
* @return MinCostMaxFlow_Node */
function other($v) {
Expand Down Expand Up @@ -333,7 +322,7 @@ private function add_downstream($v, $klass, &$a) {
if ($v->klass === $klass) {
$a[] = $v;
} else if ($v !== $this->sink) {
for ($e = $v->e1; $e; $e = $e->next($v)) {
foreach ($v->e as $e) {
if ($e->src === $v
&& $e->flow > 0
&& $e->dst->npos === 0)
Expand All @@ -359,7 +348,7 @@ private function add_upstream($v, $klass, &$a) {
if ($v->klass === $klass) {
$a[] = $v;
} else if ($v !== $this->source) {
for ($e = $v->e1; $e; $e = $e->next($v)) {
foreach ($v->e as $e) {
if ($e->dst === $v
&& $e->flow > 0
&& $e->src->npos === 0)
Expand Down Expand Up @@ -390,7 +379,7 @@ function reachable($v, $klass) {
private function topological_sort_visit($v, $klass, &$a) {
if ($v !== $this->sink && $v->npos === 0) {
$v->npos = 1;
for ($e = $v->e1; $e; $e = $e->next($v)) {
foreach ($v->e as $e) {
if ($e->src === $v && $e->flow > 0 && $e->dst->npos === 0)
$this->topological_sort_visit($e->dst, $klass, $a);
}
Expand Down Expand Up @@ -422,16 +411,14 @@ function topological_sort($v, $klass) {

private function initialize_edges() {
foreach ($this->v as $v) {
$v->e1 = null;
$v->e = [];
}
// all sources must come before all destinations
foreach ($this->e as $e) {
$e->next_dst = $e->dst->e1;
$e->dst->e1 = $e;
$e->src->e[] = $e;
}
foreach ($this->e as $e) {
$e->next_src = $e->src->e1;
$e->src->e1 = $e;
$e->dst->e[] = $e;
}
$this->has_edges = true;
}
Expand All @@ -445,7 +432,7 @@ private function initialize_edges() {
private static function pushrelabel_bfs_setdistance($qtail, $v, $dist) {
if ($v->distance !== $dist) {
$v->distance = $dist;
$v->epos = $v->e1;
$v->npos = 0;
}
$v->xlink = null;
$qtail->xlink = $v;
Expand All @@ -461,7 +448,7 @@ private function pushrelabel_make_distance() {
$qhead->xlink = null;
while ($qhead) {
$d = $qhead->distance + 1;
for ($e = $qhead->e1; $e; $e = $e->next($qhead)) {
foreach ($qhead->e as $e) {
if ($e->residual_cap_to($qhead) > 0
&& $e->other($qhead)->xlink === $this->sink)
$qtail = self::pushrelabel_bfs_setdistance($qtail, $e->other($qhead), $d);
Expand All @@ -482,28 +469,30 @@ private function pushrelabel_push_from($e, $src) {
/** @param MinCostMaxFlow_Node $v */
private function pushrelabel_relabel($v) {
$d = INF;
for ($e = $v->e1; $e; $e = $e->next($v)) {
foreach ($v->e as $e) {
if ($e->residual_cap_from($v) > 0)
$d = min($d, $e->other($v)->distance + 1);
}
//fwrite(STDERR, "relabel {$v->name}@{$v->distance}->{$d}\n");
$v->distance = $d;
$v->epos = $v->e1;
$v->npos = 0;
}

/** @param MinCostMaxFlow_Node $v */
private function pushrelabel_discharge($v) {
$ne = count($v->e);
$relabeled = false;
while ($v->excess > 0 && $v->distance < INF) {
if (($e = $v->epos)) {
if ($v->npos === $ne) {
$this->pushrelabel_relabel($v);
$relabeled = true;
} else {
$e = $v->e[$v->npos];
if ($e->is_distance_admissible_from($v)) {
$this->pushrelabel_push_from($e, $v);
} else {
$v->epos = $v->epos->next($v);
++$v->npos;
}
} else {
$this->pushrelabel_relabel($v);
$relabeled = true;
}
}
return $relabeled;
Expand All @@ -515,7 +504,7 @@ private function pushrelabel_run() {
// initialize preflow
foreach ($this->v as $v) {
$v->distance = count($this->v);
$v->epos = $v->e1;
$v->npos = 0;
}
$this->pushrelabel_make_distance();
foreach ($this->e as $e) {
Expand Down Expand Up @@ -627,8 +616,8 @@ private function cspushrelabel_push_from($e, $src) {
private function cspushrelabel_relabel($v) {
// calculate new price
$p = -INF;
$eex = null;
for ($e = $v->e1; $e; $e = $e->next($v)) {
$ex = 0;
foreach ($v->e as $epos => $e) {
if ($e->src === $v && $e->flow < $e->cap) {
$px = $e->dst->price - $e->cost;
} else if ($e->dst === $v && $e->flow > $e->mincap) {
Expand All @@ -638,12 +627,12 @@ private function cspushrelabel_relabel($v) {
}
if ($px > $p) {
$p = $px;
$eex = $e;
$ex = $epos;
}
}
assert($p != -INF || $v->excess == 0);
if ($p > -INF) {
$v->epos = $eex;
$v->npos = $ex;
} else {
$p = $v->price;
}
Expand All @@ -655,15 +644,16 @@ private function cspushrelabel_relabel($v) {

/** @param MinCostMaxFlow_Node $v */
private function cspushrelabel_discharge($v) {
$ne = count($v->e);
while ($v->excess > 0) {
if (!$v->epos || !$v->n_outgoing_admissible) {
if ($v->npos === $ne || !$v->n_outgoing_admissible) {
$this->cspushrelabel_relabel($v);
} else {
$e = $v->epos;
$e = $v->e[$v->npos];
if ($e->is_price_admissible_from($v)) {
$this->cspushrelabel_push_from($e, $v);
} else {
$v->epos = $e->next($v);
++$v->npos;
}
}
}
Expand Down Expand Up @@ -697,7 +687,7 @@ private function cspushrelabel_reprice() {
if ($v->distance !== $bi) {
continue;
}
for ($e = $v->e1; $e; $e = $e->next($v)) {
foreach ($v->e as $e) {
if ($e->residual_cap_to($v)
&& ($dst = $e->other($v))
&& $bi < $dst->distance) {
Expand Down Expand Up @@ -746,28 +736,20 @@ private function cspushrelabel_refine($phaseno, $nphases) {
if (max(abs($this->mincost), $this->maxcost) >= $fixbound) {
$ndropped = 0;
foreach ($this->v as $v) {
$eprev = null;
$e = $v->e1;
while ($e) {
$enext = $e->next($v);
for ($i = 0; $i < count($v->e); ) {
$e = $v->e[$i];
if (abs($e->reduced_cost(false)) >= $fixbound) {
if ($e->is_price_admissible_from($v)) {
--$v->n_outgoing_admissible;
}
if ($eprev === null) {
$v->e1 = $enext;
} else if ($v === $eprev->src) {
$eprev->next_src = $enext;
} else {
$eprev->next_dst = $enext;
}
$v->epos = $v->e1; // keep epos in bounds
$v->e[$i] = $v->e[count($v->e) - 1];
array_pop($v->e);
$v->npos = 0; // keep npos in bounds
$this->has_edges = false;
++$ndropped;
} else {
$eprev = $e;
++$i;
}
$e = $enext;
}
}
$this->debug && $ndropped && fwrite(STDERR, "dropedge $ndropped\n");
Expand All @@ -784,7 +766,7 @@ private function cspushrelabel_refine($phaseno, $nphases) {
// saturate negative-cost arcs
foreach ($this->v as $v) {
if ($v->n_outgoing_admissible) {
for ($e = $v->e1; $e; $e = $e->next($v)) {
foreach ($v->e as $e) {
if ($e->is_price_admissible_from($v)) {
$delta = ($e->src === $v ? $e->cap : $e->mincap) - $e->flow;
$e->update_flow($delta);
Expand All @@ -797,7 +779,7 @@ private function cspushrelabel_refine($phaseno, $nphases) {
// initialize lists and neighbor position
$lhead = $this->ltail = null;
foreach ($this->v as $v) {
$v->epos = $v->e1;
$v->npos = 0;
if ($v->excess > 0) {
$this->ltail ? ($this->ltail->link = $v) : ($lhead = $v);
$v->link = null;
Expand Down Expand Up @@ -930,11 +912,10 @@ function reset() {
if ($this->hasrun) {
foreach ($this->v as $v) {
$v->distance = $v->excess = $v->price = 0;
$v->e1 = $v->epos = null;
$v->e = [];
}
foreach ($this->e as $e) {
$e->flow = 0;
$e->next_src = $e->next_dst = null;
}
$this->maxflow = null;
$this->maxflow_start_at = $this->maxflow_end_at = null;
Expand All @@ -948,7 +929,7 @@ function clear() {
// break circular references
foreach ($this->v as $v) {
$v->link = $v->xlink = null;
$v->e1 = $v->epos = null;
$v->e = [];
}
$this->v = [];
$this->e = [];
Expand Down Expand Up @@ -1065,7 +1046,7 @@ private function dimacs_output($flags) {
if ($e->flow) {
// is this flow ambiguous?
$n = 0;
for ($ee = $e->src->e1; $ee; $ee = $ee->next($e->src)) {
foreach ($e->src->e as $ee) {
if ($ee->dst === $e->dst)
++$n;
}
Expand Down Expand Up @@ -1145,7 +1126,7 @@ function parse_dimacs($str) {
$src = $this->dimacs_node($vnames, intval($m[1]));
$dst = $this->dimacs_node($vnames, intval($m[2]));
$found = false;
for ($e = $src->e1; $e; $e = $e->next($src)) {
foreach ($src->e as $e) {
if ($e->dst === $dst
&& ($next_cap === null || $e->cap === $next_cap)
&& ($next_cost === null || $e->cost === $next_cost)) {
Expand Down

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