Program: 72742
Project: 72742
Buggy source:
/** 
 * Update the calculation of the next output time and request a refiring at that time. If there is a new input, read it and update the slope.
 * @return True if the base class returns true.
 * @throws IllegalActionException If reading inputs or parameters fails.
 */
public boolean postfire() throws IllegalActionException {
  Time currentTime=getDirector().getModelTime();
  for (int i=0; i < dx.size(); i++) {
    if (dx.get(i).hasToken(0)) {
      u[i]=dx.get(i).get(0);
      if (!u[i].equals(previousInput[i])) {
        previousInput[i]=u[i];
        slope[i]=((DoubleToken)u[i]).doubleValue();
        inputReceived[i]=true;
      }
    }
    if (currentTime.equals(nextOutputTime[i]) || nextOutputTime[i] == null) {
      if (nextOutputTime[i] != null) {
        x[i]=nextOutputValue[i];
      }
      previousOutputValue[i]=nextOutputValue[i];
      nextOutputTime[i]=_nextCrossingTime(slope[i],0.0,0.0,dq[i],currentTime);
    }
 else {
      if (inputReceived[i]) {
        x[i]+=slope[i] * (currentTime.subtract(previousStateUpdateTime[i])).getDoubleValue();
        System.out.println("String_Node_Str" + String.valueOf(i) + "String_Node_Str"+ String.valueOf((x[i])));
        nextOutputTime[i]=_nextCrossingTime(slope[i],x[i],nextOutputValue[i],dq[i],currentTime);
        inputReceived[i]=false;
      }
    }
    nextOutputValue[i]=_nextOutputValue(slope[i],previousOutputValue[i],dq[i]);
    previousStateUpdateTime[i]=nextOutputTime[i];
  }
  _minNextCrossingTime();
  if (t_min != Time.POSITIVE_INFINITY) {
    getDirector().fireAt(this,t_min);
    for (int j=0; j < dx.size(); j++) {
      for (int i=0; i < index_min.size(); i++) {
        if (j == index_min.get(i)) {
          previousStateUpdateTime[j]=t_min;
        }
      }
    }
  }
  return super.postfire();
}

Fixed version (ground truth):
/** 
 * Update the calculation of the next output time and request a refiring at that time. If there is a new input, read it and update the slope.
 * @return True if the base class returns true.
 * @throws IllegalActionException If reading inputs or parameters fails.
 */
public boolean postfire() throws IllegalActionException {
  Time currentTime=getDirector().getModelTime();
  for (int i=0; i < dx.size(); i++) {
    if (dx.get(i).hasToken(0)) {
      u[i]=dx.get(i).get(0);
      if (!u[i].equals(previousInput[i])) {
        previousInput[i]=u[i];
        slope[i]=((DoubleToken)u[i]).doubleValue();
        inputReceived[i]=true;
      }
    }
    if (currentTime.equals(nextOutputTime[i]) || nextOutputTime[i] == null) {
      if (nextOutputTime[i] != null) {
        x[i]=nextOutputValue[i];
      }
      previousOutputValue[i]=nextOutputValue[i];
      nextOutputTime[i]=_nextCrossingTime(slope[i],0.0,0.0,dq[i],currentTime);
    }
 else {
      if (inputReceived[i]) {
        x[i]+=slope[i] * (currentTime.subtract(previousStateUpdateTime[i])).getDoubleValue();
        System.out.println("String_Node_Str" + String.valueOf(i) + "String_Node_Str"+ String.valueOf((x[i])));
        nextOutputTime[i]=_nextCrossingTime(slope[i],x[i],nextOutputValue[i],dq[i],currentTime);
        inputReceived[i]=false;
      }
    }
    nextOutputValue[i]=_nextOutputValue(slope[i],previousOutputValue[i],dq[i]);
    previousStateUpdateTime[i]=currentTime;
  }
  _minNextCrossingTime();
  if (t_min != Time.POSITIVE_INFINITY) {
    getDirector().fireAt(this,t_min);
    for (int j=0; j < dx.size(); j++) {
      for (int i=0; i < index_min.size(); i++) {
        if (j == index_min.get(i)) {
          previousStateUpdateTime[j]=t_min;
        }
      }
    }
  }
  return super.postfire();
}