Dear Joshua,
There are a number of problems with your example.
- You never call a solver
- You don't encapsulate your CSP in a script (your proc Dinner is not a
script!)
- You post constraints after calling FD.distribute
...
You may want to read the Finite Domain Constraint Programming tutorial
first (you are actually citing it, so I wonder..).
I also suggest first trying something out in the OPI before writing an
application.
Best,
Torsten
On 20.04.2007, at 17:50, Joshua ben Jore wrote:
I am having difficulty writing a very simple little constraint
program. When I use FD.distribute my program stops. When I manually
set values that haven't been completely constrained yet, I get invalid
results (unless I *reassert* a constraint).
I'm certain I'm doing something wrong.
{Dinner 20} returns the following where I expect a tuple of unique
values. This is just ordering the numbers 1..20 by the rules in the
solver.
dinner(_{1#19} _{2#19} _{3#19} _{4#19} _{5#19} _{6#19} _{7#19} _{8#19}
_{9#19} _{10#19} _{11#19} _{12#20} _{1#20} _{1#20} _{1#20}
_{1#20} 1 _{1#19} _{2#20} _{1#20})
If I use FD.distribute then my solver's execution stops. Wha? I don't
much care *how* it picks solutions, I just want it to pick some
solutions.
If I try to set all variables to their minimum, I get this invalid
result. I *hoped* that the range for each variable would adjust as I
modified other variables they were constrained against. I don't see
why I have a pile of values all '2'.
dinner(2 3 4 5 6 7 8 9 10 11 12 13 2 2 2 2 1 2 3 2)
If I use that previous loop but reassert FD.distinct then it actually
finds a solution. Huh? Didn't I already assert FD.distinct? Why should
I have to reassert it? Did it forget?
Any help understanding my problem would be most appreciated. I have
read http://www.mozart-oz.org/documentation/fdt/node52.html but don't
see an immediate application. All my domains are finite and specified
- they're just not getting solved.
Thanks in advance,
Josh.
%% Example program follows:
functor
import
Application
System
FD
Property
Browser
define
proc {LeftOf X Y}
X <: Y
end
proc {ImmediatelyLeft X Y}
X =: Y - 1
end
proc {Dinner NumGuests Guests}
{FD.tuple dinner NumGuests 1#NumGuests Guests}
{FD.distinct Guests}
%% Guests 1 to 12 sit left of each other with people possibly
%% between them.
for L in 1..11 do
R
in
R = L + 1
{LeftOf Guests.L Guests.R}
end
%% 17th guest is in seat 1
Guests.17 =: 1
%% 18 is immediately to the left of 19.
{ImmediatelyLeft Guests.18 Guests.19}
end
Sol
in
{Property.put 'print.width' 100}
{Dinner 20 Sol}
{Browser.browse Sol}
{System.show Sol}
%%% Appears to begin waiting for something. What?
%%{FD.distribute ff Sol}
%%% Also appears to wait for something.
%% {FD.assign min Sol}
%% Produces invalid results?! At least it finishes. I'm *Sure
for I in 1..20 do
Min Max
in
%% More than one possible solution for this variable?
Min = {FD.reflect.min Sol.I}
Max = {FD.reflect.max Sol.I}
if Min \= Max then
Sol.I = Min
%% Works if I reassert this.
{FD.distinct Sol}
end
end
{System.show Sol}
{Application.exit 0}
end
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--
Torsten Anders
Sonic Arts Research Centre • Queen's University Belfast
Frankstr. 49 • D-50996 Köln
Tel: +49-221-3980750
http://strasheela.sourceforge.net
http://www.torsten-anders.de
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