code: protected void varBumpActivity(int v, double inc) {
      final MSVariable var = this.vars.get(v);
      var.incrementActivity(inc);
      if (var.activity() > 1e100) {
        for (final MSVariable variable : this.vars)
          variable.rescaleActivity();
        this.varInc *= 1e-100;
      }
      if (this.orderHeap.inHeap(v))
        this.orderHeap.decrease(v);
    }
docs: Bumps the activity of the variable at a given index by a given value.
  @param v   the variable index
  @param inc the increment value