What you learn today
- Maximum without a match returns ninf
- Minimum returns 0
- Guard with Count
Two sensors hang in the battery room. Cooling should start as soon as one of them reports more than 35 °C. So Maximum. That works until someone removes both sensors for a rebuild. Then the display shows “−Infinity”, the cooling stands still, and nobody notices.
Three answers to “no match”
| Mode | result without a device |
|---|---|
Average | NaN |
Minimum | 0 |
Maximum | −infinity (ninf) |
That is how the game code is built: Minimum catches the empty case and returns 0, Maximum does not. It keeps its start value of −infinity.
Why −infinity is dangerous
−infinity is a number, not NaN. snan does not trigger, and every comparison behaves perfectly normally:
lbn highest SENSOR HASH("Akkuraum") Temperature Maximum
sgt cool highest ON # -inf > 308.15: never trueThe cooling stays off. For an overheating battery room that is the wrong direction. If you keep calculating, it does not get better: −infinity minus 273.15 stays −infinity, and the display shows nonsense.
Minimum has its trap too: 0 is a valid reading. 0 K does not happen, but a pressure of 0 kPa does. Without a device a pressure minimum looks like a vacuum.
Guarding with Count
Before you believe the maximum, you ask whether any device is there at all:
lb count SENSOR PrefabHash Count
seqz missing count # 1 = no sensor
or cool cool missing # no sensor: coolCount ignores the name, you know that since yesterday. If other gas sensors hang on the network, take the sum over PrefabHash divided by the hash. Or compare with ninf directly:
seq missing highest ninf # -inf only happens without a sensorThe comparison with ninf is exact and works because −infinity is exactly equal to −infinity.
Never rely on Maximum reporting anything sensible when the sensors are missing. Every line that uses the maximum needs a guard in front of it.
For the display replace the empty case with a clear value such as −999. A player understands “−999” faster than “−Infinity”.
Diagram
Exercise
Task
Two gas sensors “Akkuraum” (there are no other gas sensors on the network). The code in the editor already uses Maximum but is not guarded.
- wall cooler “Akkukuehler”: on above 35 °C, off below 30 °C (highest temperature)
- if no sensors are present: cooler on, flashing light “Akkuwarnung” on
- LED “Akkutemp” shows the highest temperature in °C, without a sensor −999
Hints
Hint 1
lb count SENSOR PrefabHash Count, then seqz missing count.
Hint 2
Add or cool cool missing to the hysteresis.
Hint 3
Switch the warning lamp directly with missing, the display with select c missing NOVALUE c.
Quiz
4 questions. You pass from 60 % – the server does the grading.
Complete the day
- Passed the simulator exercise
- Passed the quiz with at least 60 %
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