============================================================
  iZplus (iZplus)
     -- iZ based solver for MiniZinc Challenge 2022 --

  Copyright (C) 2012-2022 NTT DATA SEKISUI SYSTEMS CORPORATION.
============================================================

* What is iZplus

  iZplus is a FlatZinc solver using iZ-C constraint programming
library which is developed by NTT DATA SEKISUI SYSTEMS CORPORATION.

iZ-C provides :
  * many built-in constraints
  * constraint propagation mechanism
  * simple search strategy

And in iZplus, following algorithms are 'plus'ed.

  * Randomized restarting in search
    For fast random number generation, Xorshift128 algorithm is used.
       http://www.jstatsoft.org/v08/i14/paper

    Restart strategy is geometirc, but counter will be rewinded
    periodically like Luby strategy.

  * Local search for optimization problem
      In real world problems, sometimes finding 'good' solution using
    short time is more important than finding 'best' solution using
    long time. And it is known empirically that 'good' solutions are
    similar to each other, then local search can be a good strategy.
    
      For optimization problem, iZplus tries to find first solution
    using constraint propagation and search. After one solution was found,
    it searches similar solutions better than first one.

  * Local search for satisfying problem
      iZplus tries to maxmize count of assinged variables without
     conflict. (Local solution will be relaxed after limited restarting)

  * Variable reordering
      Failures occured while searching are recorded and variable selection
     order is changed using this information. (Last conflict variable is
     much weighted)

      "Last conflict" is described in:
       http://www.cril.univ-artois.fr/~vidal/publis/ecai06.pdf

      (Dom/Wdeg and weighted constraint count are also used.)

  * NG learning
      NG learning is implemented as described in:
        http://ijcai.org/papers07/Papers/IJCAI07-019.pdf

      (To keep NG set small, inactive NGs are removed from learnt set.)


* Author

  Toshimitsu FUJIWARA <t.fujiwara@sekisui.com>
    developer at NTT DATA SEKISUI SYSTEMS CORPORATION


* Acknowledgement

  FlatZinc parser in iZplus is based on 'FlatZinc parser skeleton'
written by Guido Tack. 

    http://www.gecode.org/flatzinc.html/

  License of FlatZinc parser skelton (part of Gecode) is: 

    Copyright:
       Guido Tack, 2007

    Permission is hereby granted, free of charge, to any person obtaining
    a copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:
  
    The above copyright notice and this permission notice shall be
    included in all copies or substantial portions of the Software.
  
    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
    LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
    OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
    WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

  Special thanks to Guido Tack and Gecode team.

  iZ-C is a constraint programming library developed by
NTT DATA SEKISUI SYSTEMS CORPORATION.

   http://www.constraint.org/en/izc_download.html