FD.distribute never returns and manual constraining fails?

[Torsten Anders]

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