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All-pairs shortest paths examples

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Tony Garnock-Jones 2016-03-08 10:53:49 +00:00
parent a7a23e29b4
commit f221063441
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prospect/examples/all-pairs-shortest-paths/all-pairs-shortest-paths.rb Normal file
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# ShortestPaths example, from figure 1 of "Logic and lattices for
# distributed programming", Conway et. al, UCB tech report, 2012
#
# Modified slightly:
# - added "bootstrap" section to give the algorithm some data
# - added "stdio <~ ..." to monitor results
# - added boilerplate to kickstart the program
#
# Problem: doesn't terminate or yield output, because cycles exist in
# the input.
require 'rubygems'
require 'bud'
class ShortestPaths
include Bud
state do
table :link, [:from, :to] => [:cost]
scratch :path, [:from, :to, :next_hop, :cost]
scratch :min_cost, [:from, :to] => [:cost]
end
bootstrap do
link <= [[1, 3, -2],
[2, 1, 4],
[2, 3, 3],
[3, 4, 2],
[4, 2, -1]]
end
bloom do
path <= link {|l| [l.from, l.to, l.to, l.cost]}
path <= (link*path).pairs(:to => :from) do |l,p|
[l.from, p.to, l.to, l.cost + p.cost]
end
min_cost <= path.group([:from, :to], min(:cost))
stdio <~ path { |p| ["path" + p.to_s] }
stdio <~ min_cost { |m| ["min_cost" + m.to_s] }
end
end
program = ShortestPaths.new()
program.run_fg

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prospect/examples/all-pairs-shortest-paths/all-pairs-shortest-paths.rkt Normal file
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#lang prospect
;; After Figure 1 in "Logic and lattices for distributed programming",
;; Conway et. al, UCB tech report, 2012
;;
;; Quasi-problem: doesn't terminate, because cycles exist in the
;; input.
(require racket/set)
(require prospect/actor)
(struct link (from to cost) #:prefab)
(struct path (from to cost) #:prefab)
(struct path-exists (from to) #:prefab) ;; Hmm.
(struct min-cost (from to cost) #:prefab)
(actor (forever (assert (link 1 3 -2))
(assert (link 2 1 4))
(assert (link 2 3 3))
(assert (link 3 4 2))
(assert (link 4 2 -1))))
(actor (forever (during (link $from $to $cost)
(assert (path-exists from to))
(assert (path from to cost)))))
(actor (forever (during (link $A $B $link-cost)
(during (path B $C $path-cost)
(assert (path-exists A C))
(assert (path A C (+ link-cost path-cost)))))))
(actor (forever (during (path-exists $from $to)
#:collect [(costs (set)) (least +inf.0)]
(assert (min-cost from to least))
(on (asserted (path from to $cost))
(values (set-add costs cost)
(min least cost)))
(on (retracted (path from to $cost))
(define new-costs (set-remove costs cost))
(values new-costs
(for/fold [(least +inf.0)] [(x new-costs)] (min x least)))))))
;; (actor (forever (during (path $from $to $cost)
;; #:init [(displayln `(+ ,(path from to cost)))]
;; #:done [(displayln `(- ,(path from to cost)))])))
(actor (forever (on (asserted (min-cost $from $to $cost))
(displayln (min-cost from to cost)))))

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prospect/examples/all-pairs-shortest-paths/all-pairs-shortest-paths2.rb Normal file
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# ShortestPaths example, from figure 1 of "Logic and lattices for
# distributed programming", Conway et. al, UCB tech report, 2012
#
# Modified slightly:
# - added "bootstrap" section to give the algorithm some data
# - added "stdio <~ ..." to monitor results
# - added boilerplate to kickstart the program
# - repurposed next_hop field to track seen-set to avoid nontermination
require 'rubygems'
require 'bud'
require 'set'
class ShortestPaths
include Bud
state do
table :link, [:from, :to] => [:cost]
scratch :path, [:from, :to, :seen, :cost]
scratch :min_cost, [:from, :to] => [:cost]
end
bootstrap do
link <= [[1, 3, -2],
[2, 1, 4],
[2, 3, 3],
[3, 4, 2],
[4, 2, -1]]
end
bloom do
path <= link {|l| [l.from, l.to, Set.new.add(l.from).add(l.to), l.cost]}
path <= (link*path).pairs(:to => :from) do |l,p|
[l.from, p.to, p.seen.clone.add(l.from), l.cost + p.cost] if not p.seen.include?(l.from)
end
min_cost <= path.group([:from, :to], min(:cost))
stdio <~ path { |p| ["path" + p.to_s] }
stdio <~ min_cost { |m| ["min_cost" + m.to_s] }
end
end
program = ShortestPaths.new()
program.run_fg

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prospect/examples/all-pairs-shortest-paths/all-pairs-shortest-paths2.rkt Normal file
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#lang prospect
;; After Figure 1 in "Logic and lattices for distributed programming",
;; Conway et. al, UCB tech report, 2012
(require racket/set)
(require prospect/actor)
(struct link (from to cost) #:prefab)
(struct path (from to seen cost) #:prefab)
(struct path-exists (from to) #:prefab) ;; Hmm.
(struct min-cost (from to cost) #:prefab)
(actor (forever (assert (link 1 3 -2))
(assert (link 2 1 4))
(assert (link 2 3 3))
(assert (link 3 4 2))
(assert (link 4 2 -1))))
(actor (forever (during (link $from $to $cost)
(assert (path-exists from to))
(assert (path from to (set from to) cost)))))
(actor (forever (during (link $A $B $link-cost)
(during (path B $C $seen $path-cost)
(assert #:when (not (set-member? seen A)) (path-exists A C))
(assert #:when (not (set-member? seen A))
(path A C (set-add seen A) (+ link-cost path-cost)))))))
(actor (forever (during (path-exists $from $to)
#:collect [(costs (set)) (least +inf.0)]
(assert (min-cost from to least))
(on (asserted (path from to _ $cost))
(values (set-add costs cost)
(min least cost)))
(on (retracted (path from to _ $cost))
(define new-costs (set-remove costs cost))
(values new-costs
(for/fold [(least +inf.0)] [(x new-costs)] (min x least)))))))
(actor (forever (during (path $from $to $seen $cost)
#:init [(displayln `(+ ,(path from to seen cost)))]
#:done [(displayln `(- ,(path from to seen cost)))])))
(actor (forever (on (asserted (min-cost $from $to $cost))
(displayln (min-cost from to cost)))))