Machine Learning Recruiter
This page documents the new machine learning recruiter submitted as a patch for Wesnoth 1.11. We describe how to run it, discuss experiment showing that the ML Recruiter achieves dramatically better performance than the RCA AI recruiter, describe known issues and suggest a development road map.
Note that the ML Recruiter is a work in progress. We welcome feedback on it. Please discuss it on the thread "Machine Learning Recruiter" at http://forums.wesnoth.org/viewtopic.php?f=10&t=36642.
Contents
Why include ML Recruiter in Wesnoth?
The ML Recruiter makes use of a small subset of the Waffles Machine Learning toolkit adding 13 pairs of .cpp/.h files to Wesnoth. In addition, the neural nets used by ML Recruiter are serialized as .json files, which is a format Wesnoth has not yet contained. So why is this patch worthwhile?
Why the ML Recruiter will be great for Wesnoth
- Performance is great. ML Recruiter defeats RCA AI 70 - 71% of the time. Although we don't have data, this should translate into better performance against humans
- This superior performance is achieved with comparable "fun factor"
- Variety of units recruited by recommended ML Recruiter is comparable to or better than RCA AI
- Don't need to eliminate RCA AI recruiter. Campaign designers can choose to use one or the other
- ML Recruiter should be easier to customize than RCA AI because
- All core logic is in Lua, which is easier to modify than existing C++
- Performance "out of the box" on known units likely to be strong
- When new recruitable units are introduced by campaign designers, it can be trained by running c. 600 games in two hours. The new model is included as a .json file with the campaign data
- Plug and play architecture of machine learning "features" easily allows minor modifications to mainline recruiter or to campaign-specific recruiters
- Easy way to adjust campaign difficulty: Adjusting ML AI for more/less randomness makes is easier/harder to defeat
- Inclusion of ML Recruiter could lead to greater publicity and more contributors to Wesnoth
- SeattleDad plans to submit this work as a scientific paper to a conference such as Computational Intelligence in Games
- Others might later build on this work by, for instance, trying ML algorithms other than neural nets, adding new features, further generalizing the algorithm, etc.
- The machine learning infrastructure is not specific to recruiting and could be repurposed for, for instance, attack planning, weapon selection, and making "retreat and heal" vs. "attack" decisions
- All of the above is potentially publishable research, so Wesnoth could attract contributions from computer science graduate students
- Note that, having established the basic framework with this patch, future work on machine learning will be much easier
Using ML Recruiter
Applying the patch
- Get the patch from https://gna.org/patch/?3479
- Get the Wesnoth 1.11 source as per http://wesnoth.org
- Apply the patch as follows:
patch -p1 -i [path to patch file]
- Compile Wesnoth using CMake, SCons, or XCode
Playing against the ML Recruiter
- From the main menu, choose "Multiplayer"
- Choose "Local Game"
- Pick a map and adjust settings as desired. ML Recruiter has been trained with the default setting for village gold and support, but it should work fine on other settings
- Hit Okay
- For one side, Choose Player/Type-->Computer Player and then either ML AI (Recommended) or ML AI (Pure)
- For the opponent, either play against it yourself (pick your name) or watch it play the default AI (Computer Player-->RCA AI)
Watching the ML Recruiter play a single game in nogui mode
The following command is convenient for watching the ML Recruiter play a single game in nogui mode, which allows you to quickly and easily see the ML Recruiter's decision-making process. In this example, we would be running the ML AI (Recommended mode) for the Knalgan Alliance, while the default AI would be playing the Undead
Wesnoth --log-info=ai/testing,ai/ml --nogui --multiplayer --controller 1:ai --controller 2:ai --parm 1:gold:100 --parm 2:gold:100 --parm 1:village_gold:2 --parm 2:village_gold:2 --scenario multiplayer_The_Freelands --ai-config 1:ai/ais/ml_ai_faction_specific_weighted_random.cfg --ai-config 2:ai/dev/default_ai_with_recruit_log.cfg --side 1:"Knalgan Alliance" --side 2:Undead
Testing the ML Recruiter in batch mode
Testing in batch mode is easy. After applying the ML Recruiter patch, copy utils/ai_test/ai_test2.cfg to the directory in which you want to run the experiment. Then edit the first line of the .cfg file, "path_to_wesnoth_binary" to point to your Wesnoth executable. Then adjust faction1 and faction2 to point to the factions you want to experiment with and point ai_config1 at the ML configuration file you want to try out. Finally, to make everything easier, add the following to your path:
[Wesnoth_Install]/utils/ai_test/
Now you can test Wesnoth in batch as follows:
ai_test2.py ai_test2.cfg
Experiments: ML Recruiter vs. RCA AI Recruiter
Chart showing relative winning percentages
- RCA AI: The Default AI. Wins 50% of the time against itself (of course)
- Random: Recruiting units are chosen completely at random. Wins 45.5% of the time overall
- Recommended ML Recruiter: Units are chosen at random weighted by their relative value. Wins 70% overall.
- Pure ML Recruiter: ML AI always chooses the unit it thinks is best. Wins 71.5% of the time overall, but is might be seen as boring since it can produce armies which are overwhelmingly one or two units.
Chart showing winning percentage of RCA AI, Random, Recommended, and pure ML Recruiters
Winning percentages for Recommended ML Recruiter
$ analyze_log.py *.log
Overall Stats
Win % Wins AI
30.0% 1076 "default_ai_with_recruit_log
70.0% 2506 "ml_ai_faction
Total: 3582
Win Lose Win %
Drakes vs Undead 37 43 46.2%
Drakes vs Northerners 44 75 37.0%
Drakes vs Loyalists 69 17 80.2%
Drakes vs Knalgan Alliance 52 54 49.1%
Drakes vs Drakes 66 40 62.3%
Drakes vs Rebels 77 17 81.9%
Total Drakes 345 246 58.4%
Knalgan Alliance vs Undead 74 19 79.6% Knalgan Alliance vs Northerners 29 73 28.4% Knalgan Alliance vs Loyalists 93 16 85.3% Knalgan Alliance vs Knalgan Alliance 67 37 64.4% Knalgan Alliance vs Drakes 83 39 68.0% Knalgan Alliance vs Rebels 75 18 80.6% Total Knalgan Alliance 421 202 67.6%
Loyalists vs Undead 25 73 25.5% Loyalists vs Northerners 24 67 26.4% Loyalists vs Loyalists 73 20 78.5% Loyalists vs Knalgan Alliance 57 50 53.3% Loyalists vs Drakes 61 27 69.3% Loyalists vs Rebels 55 48 53.4% Total Loyalists 295 285 50.9%
Northerners vs Undead 91 5 94.8% Northerners vs Northerners 72 26 73.5% Northerners vs Loyalists 91 2 97.8% Northerners vs Knalgan Alliance 83 2 97.6% Northerners vs Drakes 67 12 84.8% Northerners vs Rebels 107 6 94.7% Total Northerners 511 53 90.6%
Rebels vs Undead 81 19 81.0% Rebels vs Northerners 34 64 34.7% Rebels vs Loyalists 97 6 94.2% Rebels vs Knalgan Alliance 92 23 80.0% Rebels vs Drakes 68 32 68.0% Rebels vs Rebels 84 14 85.7% Total Rebels 456 158 74.3%
Undead vs Undead 65 29 69.1% Undead vs Northerners 39 42 48.1% Undead vs Loyalists 108 9 92.3% Undead vs Knalgan Alliance 94 9 91.3% Undead vs Drakes 90 19 82.6% Undead vs Rebels 82 24 77.4% Total Undead 478 132 78.4%
Units recruited by Recommended ML Recruiter
Unit recruitment statistics for Drakes % Number Unit 18.5% 2256 Drake Burner 6.9% 841 Drake Clasher 15.2% 1853 Drake Fighter 19.8% 2416 Drake Glider 16.4% 1994 Saurian Augur 23.2% 2821 Saurian Skirmisher Total: 12181
Unit recruitment statistics for Knalgan Alliance % Number Unit 16.1% 2484 Dwarvish Fighter 4.7% 725 Dwarvish Guardsman 19.2% 2963 Dwarvish Thunderer 5.1% 782 Dwarvish Ulfserker 26.1% 4020 Footpad 2.5% 379 Gryphon Rider 12.1% 1862 Poacher 14.1% 2178 Thief Total: 15393
Unit recruitment statistics for Loyalists % Number Unit 25.7% 3814 Bowman 4.3% 646 Cavalryman 13.0% 1929 Fencer 6.8% 1011 Heavy Infantryman 7.4% 1093 Horseman 2.1% 308 Mage 10.4% 1546 Merman Fighter 30.4% 4522 Spearman Total: 14869
Unit recruitment statistics for Northerners % Number Unit 9.3% 1394 Goblin Spearman 1.6% 242 Naga Fighter 23.7% 3544 Orcish Archer 1.1% 168 Orcish Assassin 20.2% 3026 Orcish Grunt 39.4% 5901 Troll Whelp 4.6% 692 Wolf Rider Total: 14967
Unit recruitment statistics for Rebels % Number Unit 15.4% 2151 Elvish Archer 40.9% 5730 Elvish Fighter 11.3% 1576 Elvish Scout 2.1% 294 Elvish Shaman 3.5% 496 Mage 3.7% 523 Merman Hunter 23.1% 3236 Wose Total: 14006
Unit recruitment statistics for Undead % Number Unit 16.7% 2696 Dark Adept 9.2% 1475 Ghost 1.1% 180 Ghoul 43.2% 6966 Skeleton Archer 13.7% 2206 Skeleton 9.2% 1475 Vampire Bat 6.9% 1113 Walking Corpse Total: 16111
How the ML Recruiter works
When it's deciding what to recruit, the ML Recruiter works by predicting a "metric" which is a measure of how well a given unit will do in the game in the current situation. A good measure of a unit's usefulness is a tricky question and we will discuss three different metrics below, but let's start with the easiest one, which is the sum of the following quantities for each unit:
- Experience points at the end of the game or when the unit is killed
- Number of villages captured by the unit
Note that the ML Recruiter is blind to other ways a unit can help you (in particular, it doesn't know about poison, healing, and slowing).
This sum, which we'll call the "metric" is then divided by the unit cost to get metric/cost (think of this as goodness per unit of gold). You can see this in the debugging output that the ML Recruiter current prints to stdout:
unit type metric cost wt cost weighted metric Elvish Shaman 8.58 15 15.00 0.57 Elvish Fighter 10.42 14 14.00 0.74 Elvish Scout 8.47 18 18.00 0.47 Wose 17.07 20 20.00 0.85 Mage 10.37 20 20.00 0.52 Elvish Archer 8.46 17 17.00 0.50 Merman Hunter 8.55 15 15.00 0.57
This is from the first turn of a game between the Rebels and the Undead. The ML Recruiter is predicting that if it recruits a Wose now, it will end with 17.07 XP + Village Captures. 17.07/20 = 0.85, which is the highest weighted metric at this time, so it picks a Wose as it's top choice.
How does it know to pick a Wose? It looks at the "features" which describe the current situation. Here's another chart from the same game:
unit type metric cost wt cost weighted metric Elvish Shaman 7.18 15 15.00 0.48 Elvish Fighter 11.82 14 14.00 0.84 Elvish Scout 7.91 18 18.00 0.44 Wose 15.53 20 20.00 0.78 Mage 9.11 20 20.00 0.46 Elvish Archer 9.38 17 17.00 0.55 Merman Hunter 8.36 15 15.00 0.56 Side: 1 Gold: 21 Unit we want: Elvish Fighter PRERECRUIT:, enemy Dark Adept:1 , enemy Deathblade:1 , enemy Ghost:2 , enemy Skeleton:3 , enemy faction:Undead , enemy gold:10 , enemy level3+:0 , enemy total-gold:139 , enemy unit-gold:129 , friendly Elvish Captain:1 , friendly Elvish Fighter:1 , friendly Wose:4 , friendly faction:Rebels , friendly gold:21 , friendly level3+:0 , friendly total-gold:161 , friendly unit-gold:140 , side:1 , terrain-forest:0.082 , terrain-mountain-hill:0.113 , terrain-water-swamp:0.164 , total-gold-ratio:0.537 , turn:4 , village-control-margin:-2 , village-control-ratio:0.417 , village-enemy:7 , village-friendly:5 , village-neutral:4 ,
The "features" that it sees are the values following "PRERECRUIT". The ML AI sees that the enemy faction is the Undead and that they have one Deathblade, two ghosts, three Skeletons. The Rebels currently have 4 Wose, 1 Elvish Fighter, and 1 Elvish Captain. It also sees a number of other features like how much gold it and its opponent have, what percentage of each the map is covered by different terrain, and how many friendly, neutral, and enemy villages there are. In this situation, although it still sees that the Wose is likely to score higher on the XP + village capture metric (15.5 vs. 11.8), this isn't enough to overcome the price differential, so it chooses an Elvish Fighter as it's best choice with a weighted metric of 0.84.
Note that these predictions of 15.5 vs. 11.8 are computed by the neural net based on a model built from what the algorithm has seen has happened in similar situations during training.
Unit Goodness Metrics
We have experimented with three different unit goodness metrics. All of these metrics are designed to have the property that the higher the value of the metric, the better the unit performed in a a given game. Clearly there is a random element here. In some games when playing against a Skeleton-heavy Undead army, an Elvish Archer, which uses mainly a pierce attack may get lucky and do better than a Wose, which has an impact attack, but on average the metric should show that the Wose performs better.
The three metrics we've looked at are as follows:
Experience Point plus Village Capture
This is the metric used in ML Recruiter 0.2. As noted above, it is the sum of the following quantities:
- Experience points at the end of the game or when the unit is killed
- Number of villages captured by the unit
This metric has the advantage that experience points lead to promotion, which is a very good thing. Also, getting kills should be correlated with how much damage the unit is doing. Adding village captures to experience points is a little flaky, but is intended to give credit to fast units, which are more likely to capture villages.
Victory
This metric give a unit 1.0 if its side wins and 0 if its side loses. The effect is that the neural net's prediction for each unit can be seen as "what is the probability of victory if I add recruit this unit in this situation". This is the most natural of all metrics, but experimentally it hasn't performed as well in terms of leading to actual victories as picking units based on unit-based metrics. Performance has peaked at around a 59% win ratio for a victory metric vs. around 68 - 71% for the XP+VC metric. We think the problem is that the impact of recruiting a single unit of Type A vs. Type B on victory probability is very small so the neural net isn't differentiating among the choices enough.
Gold Yield
This metric is currently under development and is slated for ML Recruiter 0.3. It is the sum of the following quantities, all of which are intended to quantify a unit's usefulness in terms of how much gold it has gotten for the friendly side vs. gold damage done to the enemy side.
- Basic Damage Metric: Target unit cost * (Damage inflicted/target max HP) (Sapient's suggestion). The concept is that you cost your opponent this much gold by destroying this fraction of the unit. Obviously in any given attack, we would calculate this for both the attacker and the defender.
- Village Capture: capturing_unit.variables.ml_gold_yield += wesnoth.game_config.village_income. # My take is that it's important to credit the capturing unit for this. I'm thinking that fast units tend to get more captures than slow units at all stages of the game and this may be a way to give units credit for being fast.
- Poison: Treat the same as Basic Damage Metric by crediting for the amount of damage done in that turn. On the turn in which the unit is cured, credit the poisoner with Target Unit Cost * (8/target max HP) to reflect the damage that it would have healed if it hadn't been poisoned (obviously, lessened if it has less than 8 HP of damage)
- Slowing: When a unit is on defense and it slows the attacker, give no extra credit to the defender because the attacker just unslows at the end of its turn. When you slow a unit as the attacker, you get credit for an amount equal to all the Basic Damage Metric of the slowed unit (the slowed unit would otherwise have done twice as much damage, so you get credit for the damage it didn't do)
- Healing: healing_unit.variables.ml_gold_yield += Healed_unit_cost * (healed amount/healed unit max HP) # Directly analogous to the Basic Damage Metric
- Walking Corpse Creation: Credit a unit which gets a kill which creates a unit due to its plague ability with 8 gold (the value of a Walking Corpse)
- Leadership: Credit the leader for the bonus damage inflicted by the unit being led
- Maintenance: It seems to me that Level 0 units should get some sort of credit for the fact that they don't require maintenance. Not sure exactly how to handle this.
The Weighted Random (Recommended) Recruiter
The recommended recruiter is defined in ai/ais/ml_ai_faction_specific_weighted_random.cfg. It is called "Recommended" in the user interface. Although we are currently measuring it as performing slightly worse than "Pure" ML AI (ai/ais/ml_ai_faction_specific.cfg), (70% win percentage vs. 71.5% for the Pure version), we recommend it because it allows the player to see a greater variety of opposing units.
The weighted random printout looks like the following:
Turn 13:
unit type metric cost metric/ weighted %
cost m/c of total
Merman Hunter 1.10 15 0.07 0.0000 0.0%
Wose 1.72 20 0.09 0.0000 0.1%
Elvish Shaman 1.66 15 0.11 0.0000 0.4%
Elvish Archer 2.71 17 0.16 0.0000 4.0%
Elvish Fighter 2.54 14 0.18 0.0000 8.5%
Mage 4.18 20 0.21 0.0001 20.1%
Elvish Scout 4.60 18 0.26 0.0003 66.8%
Random Number chosen was 376
Side: 1 Gold: 27 Unit we want: Elvish Scout
PRERECRUIT:, enemy Dark Adept:2 , enemy Revenant:1 , enemy Skeleton:1 , enemy faction:Undead , enemy gold:8 ,
enemy level3+:0 , enemy total-gold:83 , enemy unit-gold:75 , friendly Elder Wose:1 , friendly Elvish Fighter:2 ,
friendly Elvish Ranger:1 , friendly Mage:1 , friendly Wose:3 , friendly faction:Rebels , friendly gold:27 ,
friendly level3+:0 , friendly total-gold:225 , friendly unit-gold:198 , side:1 , terrain-forest:0.082 ,
terrain-mountain-hill:0.113 , terrain-water-swamp:0.164 , total-gold-ratio:0.731 , turn:13 ,
village-control-margin:0 , village-control-ratio:0.5 , village-enemy:8 , village-friendly:8 , village-neutral:0 ,
This situation occurs towards the end of a game that the Rebels are winning. Note that total-gold-ratio (the ratio between the sum of gold + the value of all units on each side) is 0.731, so it's heavily in the Rebels' favor. The ML AI sees an Elvish Scout as being the best choice in this situation with a Mage in second place. The Elvish Scout is probably favored because the game is likely to be won rapidly and only a fast unit will be able to reach the enemy or reach a village fast enough to add to its "experience points + village capture" metric.
The difference with the Pure AI is Weighted Random then does the following:
- It takes every metric/cost value and raises it to the sixth power. Why? We want to magnify the differences. In this example 0.26/0.21 = 1.23, but (0.26**6)/(0.21**6) = 3.60.
- We then randomly choose a unit with a probability proportional to this weighted value which, in this case, was an Elvish Scout.
How to train your own ML Recruiter
Known issues
Bugs
- Haven't added new Waffles files to Visual C++, so it won't compile under VC++. I need some help with this.
Current Limitations
- Only tested on two-player multiplayer games. Doesn't work when there are more than two leaders on the map.
- Works optimally on the following two-player maps (trained on these)
- Weldyn Channel
- The Freelands
- Den of Onis
- Fallenstar Lake
- Tested on all other two-player maps and runs nearly as well except it crashes on the following:
- Aethermaw, Hornshark Island, Dark Forecast, Sablestone Delta, Elensefar Courtyard, Silverhead Crossing
- The ML Recruiter is currently blind to certain special abilities. It doesn't see the benefits of poisoning or slowing an enemy or healing a friendly unit, consequently it undervalues units that poison, slow, or heal. It is also blind to the benefits of leadership.
ML Recruiter development roadmap
- ML Recruiter 0.1: Initial drop
- ML Recruiter 0.1.1: Minor retraining of the model
- ML Recruiter 0.2:
- Logging messages changed from print statements to using lg::log_domain.
- Now have an explicit debug mode by running with --log-debug=ai/ml.
- Use local ai, which allows ML Recruiter to play against itself. Previously could only have ML Recruiter on one side.
- Some work on ML recruiting model (i.e. the core logic). Experimented with different training strategies, but features unchanged from 0.1.