code: protected void rebuildOrderHeap() {
      final LNGIntVector vs = new LNGIntVector();
      for (int v = 0; v < this.nVars(); v++)
        if (this.vars.get(v).decision() && this.vars.get(v).assignment() == Tristate.UNDEF)
          vs.push(v);
      this.orderHeap.build(vs);
    }
docs: Rebuilds the heap of decision variables.