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OROBWorld
WolfGoatCabbage
Commits
2e7932e0
Commit
2e7932e0
authored
3 years ago
by
Paul A. Rubin
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Added a CP solver.
parent
84e7261c
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src/wolfgoatcabbage/CP.java
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153 additions, 0 deletions
src/wolfgoatcabbage/CP.java
src/wolfgoatcabbage/WolfGoatCabbage.java
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10 additions, 0 deletions
src/wolfgoatcabbage/WolfGoatCabbage.java
with
163 additions
and
0 deletions
src/wolfgoatcabbage/CP.java
0 → 100644
+
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0
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2e7932e0
package
wolfgoatcabbage
;
import
ilog.concert.IloConstraint
;
import
ilog.concert.IloException
;
import
ilog.concert.IloIntVar
;
import
ilog.cp.IloCP
;
import
static
wolfgoatcabbage
.
Problem
.
CABBAGE
;
import
static
wolfgoatcabbage
.
Problem
.
GOAT
;
import
static
wolfgoatcabbage
.
Problem
.
ITEMCOUNT
;
import
static
wolfgoatcabbage
.
Problem
.
TMAX
;
import
static
wolfgoatcabbage
.
Problem
.
WOLF
;
/**
* CP implements a constraint programming model for the logic puzzle.
*
* @author Paul A. Rubin (rubin@msu.edu)
*/
public
final
class
CP
implements
AutoCloseable
{
/* CPO objects.
* For the variables `far` and `farmer`, value 1 signals the entity ends the
* period on the far bank while value 0 signals the entity ends the period
* on the near bank.
*/
private
final
IloCP
cp
;
// the model instance
private
final
IloIntVar
[][]
far
;
// far[t][i] is the location of item i
// at time t
private
final
IloIntVar
[][]
tFar
;
// transpose of far
private
final
IloIntVar
[]
farmer
;
// location of the farmer at time t
private
final
IloIntVar
[]
carry
;
// carry[t] is the index of the item
// carried across the river at time t
// (ITEMCOUNT if the farmer is deadheading)
private
final
IloIntVar
done
;
// the time period at which the problem
// is done
/**
* Constructor.
* @throws IloException if the model cannot be created
*/
public
CP
()
throws
IloException
{
// Instantiate the model.
cp
=
new
IloCP
();
// Create the variables.
done
=
cp
.
intVar
(
0
,
TMAX
-
1
);
far
=
new
IloIntVar
[
TMAX
][
ITEMCOUNT
+
1
];
tFar
=
new
IloIntVar
[
ITEMCOUNT
+
1
][
TMAX
];
carry
=
new
IloIntVar
[
TMAX
];
farmer
=
new
IloIntVar
[
TMAX
];
for
(
int
t
=
0
;
t
<
TMAX
;
t
++)
{
carry
[
t
]
=
cp
.
intVar
(
0
,
ITEMCOUNT
);
farmer
[
t
]
=
cp
.
boolVar
();
for
(
int
i
=
0
;
i
<
ITEMCOUNT
+
1
;
i
++)
{
far
[
t
][
i
]
=
cp
.
boolVar
();
tFar
[
i
][
t
]
=
far
[
t
][
i
];
}
}
// The objective is to minimize the time at which the trip is done.
cp
.
addMinimize
(
done
);
// All inventory is on the near bank at the end of period 0.
for
(
int
i
=
0
;
i
<
ITEMCOUNT
+
1
;
i
++)
{
cp
.
addEq
(
far
[
0
][
i
],
0
);
}
// The farmer also starts on the near bank.
cp
.
addEq
(
farmer
[
0
],
0
);
// Nothing is carried in period 0.
cp
.
addEq
(
carry
[
0
],
ITEMCOUNT
);
// The necessary condition for being done is that all items be on the
// far bank.
for
(
int
i
=
0
;
i
<
ITEMCOUNT
;
i
++)
{
cp
.
addEq
(
cp
.
element
(
tFar
[
i
],
done
),
1
);
}
// In each period, the status of the item carried (if any) flips while
// the status of other items does not change.
for
(
int
t
=
1
;
t
<
TMAX
;
t
++)
{
for
(
int
i
=
0
;
i
<
ITEMCOUNT
;
i
++)
{
IloConstraint
c1
=
cp
.
eq
(
carry
[
t
],
i
);
IloConstraint
c2
=
cp
.
eq
(
cp
.
sum
(
far
[
t
-
1
][
i
],
far
[
t
][
i
]),
1
);
IloConstraint
c3
=
cp
.
eq
(
far
[
t
-
1
][
i
],
far
[
t
][
i
]);
cp
.
add
(
cp
.
ifThenElse
(
c1
,
c2
,
c3
));
}
}
// In odd numbered periods, trips are from near bank to far bank, and only
// items on the near bank can be carried. In even numbered periods, trips
// are from far bank to near bank, and only items on the far bank can
// be carried.
for
(
int
t
=
1
;
t
<
TMAX
;
t
++)
{
int
z
=
(
t
%
2
==
0
)
?
1
:
0
;
cp
.
addEq
(
cp
.
element
(
far
[
t
-
1
],
carry
[
t
]),
z
);
}
// Until the last trip, the farmer ends up on the far bank at the end of
// odd numbered periods and the near bank at the end of even numbered
// periods. After the last trip, the farmer stays on the far bank.
for
(
int
t
=
1
;
t
<
TMAX
;
t
++)
{
IloConstraint
c1
=
cp
.
le
(
done
,
t
);
IloConstraint
c2
=
cp
.
eq
(
farmer
[
t
],
1
);
IloConstraint
c3
=
cp
.
eq
(
farmer
[
t
],
t
%
2
);
cp
.
add
(
cp
.
ifThenElse
(
c1
,
c2
,
c3
));
}
// If the wolf and goat are in the same place at the end of any period,
// the farmer must also be there. The same is true if the goat and cabbage
// are in the same place.
for
(
int
t
=
1
;
t
<
TMAX
;
t
++)
{
IloConstraint
c1
=
cp
.
eq
(
far
[
t
][
WOLF
],
far
[
t
][
GOAT
]);
IloConstraint
c2
=
cp
.
eq
(
far
[
t
][
GOAT
],
far
[
t
][
CABBAGE
]);
IloConstraint
c3
=
cp
.
eq
(
far
[
t
][
GOAT
],
farmer
[
t
]);
cp
.
add
(
cp
.
ifThen
(
c1
,
c3
));
cp
.
add
(
cp
.
ifThen
(
c2
,
c3
));
}
// Suppress solver output.
cp
.
setOut
(
null
);
}
/**
* Solves the model.
* @return the number of trips required
* @throws IloException if the solver fails
*/
public
int
solve
()
throws
IloException
{
cp
.
solve
();
return
cp
.
getIntValue
(
done
);
}
/**
* Gets the solution to the puzzle.
* @return a string displaying the solution
* @throws IloException if the solution does not exist
*/
public
String
getSolution
()
throws
IloException
{
int
nTrips
=
cp
.
getIntValue
(
done
);
double
[][]
x
=
new
double
[
nTrips
+
1
][
ITEMCOUNT
];
// Get the values of the far[][] array for actual items and trips used.
for
(
int
t
=
0
;
t
<=
nTrips
;
t
++)
{
for
(
int
i
=
0
;
i
<
ITEMCOUNT
;
i
++)
{
x
[
t
][
i
]
=
cp
.
getValue
(
far
[
t
][
i
]);
}
}
// Get the values of the carry[] array for trips actually used.
double
[]
y
=
new
double
[
nTrips
+
1
];
for
(
int
t
=
0
;
t
<=
nTrips
;
t
++)
{
y
[
t
]
=
cp
.
getValue
(
carry
[
t
]);
}
return
Problem
.
report
(
nTrips
,
x
,
y
);
}
/**
* Closes the model.
*/
@Override
public
void
close
()
{
cp
.
end
();
}
}
This diff is collapsed.
Click to expand it.
src/wolfgoatcabbage/WolfGoatCabbage.java
+
10
−
0
View file @
2e7932e0
...
...
@@ -18,6 +18,7 @@ public final class WolfGoatCabbage {
* @param args the command line arguments (ignored)
*/
public
static
void
main
(
final
String
[]
args
)
{
System
.
out
.
println
(
"Applying the MIP model."
);
try
(
MIP
model
=
new
MIP
())
{
double
z
=
model
.
solve
();
System
.
out
.
println
(
"Optimal number of trips = "
+
z
+
"."
);
...
...
@@ -26,6 +27,15 @@ public final class WolfGoatCabbage {
}
catch
(
IloException
ex
)
{
System
.
out
.
println
(
"CPLEX exception:\n"
+
ex
.
getMessage
());
}
System
.
out
.
println
(
"\nApplying the CP model:"
);
try
(
CP
model
=
new
CP
())
{
int
z
=
model
.
solve
();
System
.
out
.
println
(
"Optimal number of trips = "
+
z
+
"."
);
System
.
out
.
println
(
"Solution:"
);
System
.
out
.
println
(
model
.
getSolution
());
}
catch
(
IloException
ex
)
{
System
.
out
.
println
(
"CPOptimizer exception:\n"
+
ex
.
getMessage
());
}
}
}
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