5.0.0-beta.1 - setting Settings.init().setLCG(true) JUnit case doesn't work #1176

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1. axkr

   added

   bug

   on Nov 23, 2025
2. cprudhom commented on Nov 24, 2025

   

   cprudhom

   on Nov 24, 2025

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   Can you tell me what is the real domain of a,b,c when set to Integers ?
3. axkr commented on Nov 24, 2025

   

   axkr

   on Nov 24, 2025

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   Can you tell me what is the real domain of a,b,c when set to Integers ?

   intVar = model.intVar(//
                 expr.toString(), //
                 CHOCO_MIN_VALUE, //
                 CHOCO_MAX_VALUE);

   with

     final public static short CHOCO_MIN_VALUE = Short.MIN_VALUE / 2;
    
     final public static short CHOCO_MAX_VALUE = Short.MAX_VALUE / 2;

   👍React with 👍1Reacted by Charles Prud'homme
4. cprudhom commented on Nov 25, 2025

   

   cprudhom

   on Nov 25, 2025

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   If I convert your model to pure choco one, I got:

       @Test(groups = "lcg", timeOut = 60000)
       public void test685(){
           //{a*b + c == 2020, a + b*c == 2021}
           Model model = new Model(Settings.init().setLCG(true));
           IntVar a = model.intVar("a",Short.MIN_VALUE / 2,Short.MAX_VALUE / 2);
           IntVar b = model.intVar("b",Short.MIN_VALUE / 2,Short.MAX_VALUE / 2);
           IntVar c = model.intVar("c",Short.MIN_VALUE / 2,Short.MAX_VALUE / 2);
           a.mul(b).add(c).eq(2020).post();
           a.add(b.mul(c)).eq(2021).post();
           Solver solver = model.getSolver();
           solver.showShortStatistics();
           while (solver.solve()) {
               System.out.printf("a=%d b=%d c=%d%n", a.getValue(), b.getValue(), c.getValue());
           }
           Assert.assertEquals(solver.getSolutionCount(), 2);
       }

   I ran the tests on the current dev branch, namely 5.0.0-beta.2

   When I set lcg to false, I got the following output:

   Model[Model-0], 1 Solutions, Resolution time 0,257s, 28731 Nodes (111 616,7 n/s), 28730 Backtracks, 0 Backjumps, 28729 Fails, 0 Restarts, 207390 Propagations
   a=2021 b=0 c=2020
   Model[Model-0], 2 Solutions, Resolution time 0,281s, 30079 Nodes (107 183,1 n/s), 30077 Backtracks, 0 Backjumps, 30075 Fails, 0 Restarts, 275960 Propagations
   a=673 b=2 c=674
   Model[Model-0], 2 Solutions, Resolution time 0,296s, 31762 Nodes (107 195,0 n/s), 63521 Backtracks, 0 Backjumps, 31759 Fails, 0 Restarts, 300940 Propagations
   

   When I set it to false, I got:

   Model[Model-0], 1 Solutions, Resolution time 39,494s, 33533 Nodes (849,1 n/s), 33531 Backtracks, 0 Backjumps, 33531 Fails, 0 Restarts, 621278 Propagations
   a=673 b=2 c=674
   Model[Model-0], 2 Solutions, Resolution time 39,532s, 33556 Nodes (848,8 n/s), 33553 Backtracks, 0 Backjumps, 33552 Fails, 0 Restarts, 621643 Propagations
   a=2021 b=0 c=2020
   Model[Model-0], 2 Solutions, Resolution time 40,191s, 33557 Nodes (834,9 n/s), 33556 Backtracks, 0 Backjumps, 33554 Fails, 0 Restarts, 744676 Propagations
   

   Expect for the time required, which is related to the underlying MiniSat propagation, the solutions are found.
   So, I suppose that the test fails due to the resolution time ?
5. cprudhom commented on Nov 25, 2025

   

   cprudhom

   on Nov 25, 2025

   Last edited by cprudhom

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   Well, it seems that this simple problem is really not adapted to LCG : I tried with Chuffed and OR-Tools CP-SAT (with a minizinc model) and both of them take ages to find one solution.