Types of Environments — Static vs Dynamic vs Semi-Dynamic — Beginner-Friendly Notes
1. Definitions (exam exact wording)
- Static: environment does not change while agent is deciding. Agent can take its time.
- Dynamic: environment keeps changing while agent thinks — agent must decide quickly or the world moves on.
- Semi-dynamic: environment itself doesn't change, but its performance score changes with time (time matters).
2. Examples
| Environment | Type | Why? |
|---|---|---|
| Chess (clock paused during thought) | Static | Board frozen while you think |
| Chess with clock running | Semi-dynamic | Board frozen, but your score/time decays while you think |
| Crossword puzzle | Static | Nothing changes while you solve |
| Self-driving on a highway | Dynamic | Other cars move while you decide |
| Vacuum that pauses when robot thinks | Static (lab version) | Dynamic in real home (dirt appears, people walk) |
| Medical diagnosis from file | Static | Data file frozen |
3. Why It Matters
- Static → can plan deeply (search, logic) — no rush.
- Dynamic → needs real-time decision, continuous perception, often reactive agents; cannot do exhaustive search.
- Semi-dynamic → you must trade quality of decision vs time taken — anytime algorithms.
4. Connection to Agent Types
- Static + fully observable + deterministic → classical search works (Module 2).
- Dynamic + partially observable + stochastic → need sensors looping fast + model-based / learning agents.
5. Quick Test
Ask: "If I stop and think for 1 minute, does the world change or my score worsen?"
- No to both → static
- World changes → dynamic
- Only score worsens → semi-dynamic
6. One-Line Summary to Write in Exam
A static environment waits for the agent, a dynamic environment changes during deliberation requiring real-time response, and a semi-dynamic environment is static but time-dependent in its performance measure.
7. Quick Self-Check
- Is image classification static or dynamic?
- Why is real-time Pac-Man dynamic?
- Give a semi-dynamic example beyond chess clock.