DisequationSystem<LS>

Alastair · **Posted:** Thu May 07, 2009 9:29 pm

Hi,

Is the DisequationSystem<LS> still intended for general use? I notice it's disappeared from the list of classes in the documentation. It implements the methods from the Constraint<LS> interface as well as some other methods which appear like integer versions of the Constraint<LS> differentiation methods igetAssignDelta etc. The igetSwapDelta is especially strange as it has three arguments as opposed to the conventional two for the variables being swapped.

The main reason for the interest is the Comet Book (p.111) indicates that DisequationSystems are a more efficient way of storing series of disequations allowing constant time differentiation. The memory usage and time to close the Solver<LS> in my Disequation based model is significantly better than in an equivalent ConstraintSystem<LS> model.

The main problem I've hit is that in terms of differentiation it appears only the getAssignDelta works properly, the getSwapDelta and the getAssignDelta(var{int}[], int[]) both crash reporting an internal error. I've included an example, uncomment the differentiation calls to reproduce the errors.

Code:

import cotls;

Solver<LS> m();
var{int} array[i in 1..10](m, 1..10) := 5;
DisequationSystem<LS> D(array);
forall(i in 1..10, j in 1..10: j > i+1){
   D.post(array[i],array[j]);
}
D.close();
var{int} violations = D.violations();
m.close();
cout << array << endl;
cout << violations << endl;
cout << D.getAssignDelta(array[5],4) << endl;
array[5] := 4;
cout << violations << endl;

//cout << D.getSwapDelta(array[5], array[4]) << endl;
array[5] :=: array[4];
cout << violations << endl;

var{int} variables[0..1] = [array[1], array[2]];
int values[0..1] = [8, 6];
//cout << D.getAssignDelta(variables, values) << endl;
array[1] := 8;
array[2] := 6;
cout << violations << endl;

Thanks,
Alastair

ldm · **Joined:** Tue Nov 18, 2008 12:13 pm **Posts:** 68

I'll see what we can do for this. But it will be for 2.1 (not the upcoming final 2.0)

Alastair · **Posted:** Tue Feb 23, 2010 11:03 am

As of 2.0.1 the getSwap(var{int},var{int}) and getAssignDelta(var{int}[],int[]) seem to work fine, the getSwap(var{int},var{int},var{int},var{int}) and getAssign(var{int},int,var{int},int) still cause Internal Errors. This isn't such a problem because you can emulate their behaviour using the getAssignDelta(var{int}[],int[]).

Another bug I've found which causes a library exception: [DisequationSystem: Unknown Variable] is if you try to differentiate a variable which isn't part of the DisequationSystem. This is at odds with the way other classes (thinking primarily of ConstraintSystems) behave. They simply return a delta of 0 and don't cause an error.

Code:

import cotls;

range r = 1..5;
Solver<LS> ls();
var{int} x[i in r](ls, r) := 2;
var{int} y(ls, r) := 1;
DisequationSystem<LS> D(x);
ConstraintSystem<LS> S(ls);
forall(i in r, j in r: j > i){
   D.post(x[i],x[j]);
   S.post(x[i] != x[j]);
}
D.close();
S.close();
ls.close();

cout << D.getAssignDelta(x[1], 4) << endl;
var{int} vars[1..2] = [x[1],x[2]];
int vals[1..2] = [4,5];
cout << D.getAssignDelta(vars,vals) << endl;
cout << D.getSwapDelta(x[1],x[2]) << endl; 

// These will crash Comet
//cout << D.getAssignDelta(x[1], 4, x[2], 5) << endl;
//cout << D.getSwapDelta(x[1],x[2],x[3],x[4]) << endl;

cout << S.getAssignDelta(y,2) << endl;
//cout << D.getAssignDelta(y, 2) << endl;

Cheers,
Alastair

dynadec.com

DisequationSystem<LS>

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