From 6c4935c9c2144d4a07515322b176a6970f9575c4 Mon Sep 17 00:00:00 2001
From: ctincorvia <charlie.incorvia@gmail.com>
Date: Thu, 8 Dec 2016 16:10:10 -0600
Subject: [PATCH] Clingo implementatino of TSP

---
 clingo/README | 29 ++++++++++++++++++++++
 clingo/tsp.lp | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 clingo/README
 create mode 100644 clingo/tsp.lp

diff --git a/clingo/README b/clingo/README
new file mode 100644
index 0000000..284d335
--- /dev/null
+++ b/clingo/README
@@ -0,0 +1,29 @@
+Charles Incorvia (Ci2923)
+
+The traveling salesman problem implemented in Clingo.
+
+Clingo is a declarative programming languaged descened from Prolog.
+
+The clingo implementation is declarative, and thus not exactly the greedy algorithm, but in the background gringo is using greedy algorithms.
+
+In order to run this program, clingo 4.5.4 or later is required.
+
+It's available free here : http://potassco.sourceforge.net/ 
+
+The command to run the program is:
+
+clingo tsp.lp
+
+Clingo does not take inputs from I/O, so all of the information regarding the traveling salesman problem is within the file.
+
+The path() terms indicate the paths from city to city available to the salesman.
+The place() terms are the cities and their names.
+The const t is the number of cities the salesman is planning to visit.
+The first location variable indicates the salesman's starting city.
+
+The program will output UNSATISFIABLE if there's no way to visit all of the cities and return to the home city without visiting any cities twice.
+
+Otherwise, it will output SATISFIABLE and list the steps to the smallest possible path in the form of:
+
+travel(City, Time).
+
diff --git a/clingo/tsp.lp b/clingo/tsp.lp
new file mode 100644
index 0000000..d6be447
--- /dev/null
+++ b/clingo/tsp.lp
@@ -0,0 +1,67 @@
+% THE TRAVELING SALESMAN
+
+% All of the paths from city to city
+path(austin, houston, 238; houston, dallas, 163; dallas, austin, 212).
+
+%Paths are bidirectional
+path(City1, City2) :- path(City2, City1).
+
+% A list of all of the cities
+place(austin; houston; dallas).
+
+% number of cities on tour
+#const t=3.
+
+%start location
+location(austin, 0).
+
+% The salesman must end in his home city
+:- not location(City, t), location(City, 0).
+
+
+
+
+
+
+
+% choose where to travel at each timestep
+% there are exactly as many cities as there are timesteps
+{ travel(City, Time) : place(City) } 1 :- Time = 0..t-1.
+
+%if the salesman travels TO somewhere, he's already been there
+%this way, we can travel to our start city at the end
+visited(City, Time) :- travel(City, Time).
+
+%we can't travel to a city we've been to before
+:- travel(City, Time1), visited(City, Time2), Time1 > Time2.
+
+%you can't go anywhere there is not a path to
+:- travel(City_end, Time), location(City_start, Time), not path(City_start, City_end, _).
+
+%if you travel from somewhere too somewhere, distance happens
+distance(D) :- travel(City_end, Time), location(City_start, Time), path(City_start, City_end, D).
+
+
+%can't travel to where you already are
+:- travel(City, Time), location(City, Time).  
+
+%Traveling gets you places
+location(City, Time + 1) :-  travel(City, Time).
+
+
+%uniqueness of location
+-location(City2, T) :- location(City1, T), place(City2), City1 != City2.
+
+%commonsense intertia
+location(City, T + 1) :- location(City, T), not -location(City, T + 1), place(City), T = 0..t-1.
+
+
+% every city must be visited by the end
+:- place(City), not visited(City, _).
+
+% tell clingo to keep trying until it fins a solution with optimal distance.
+total(N) :- N = #sum{L : distance(L)}.
+#minimize{N : total(N)}.
+
+#show total/1.
+#show travel/2.
\ No newline at end of file