### buggy penalty

Second suspicion was that there was something wrong with the penalty calculation. Let’s add more test:

"""penalize having gaps between the columns"""          ! utility4^
...
def utility4 = {
val s = newState(Seq(
(0, 0), (0, 1), (0, 2), (0, 3), (0, 4), (0, 5), (0, 6))
map { Block(_, TKind) }, (10, 20), TKind :: TKind :: Nil)
agent.utility(s) must_== -36.0
} and {
val s = newState(Seq((1, 0), (1, 1), (2, 1), (2, 2))
map { Block(_, ZKind) }, (10, 20), TKind :: TKind :: Nil)
agent.utility(s) must_== -13.0
}

And it fails.

[error] x penalize having gaps between the columns
[error]    '-4.0' is not equal to '-13.0' (AgentSpec.scala:35)

Before we go into the REPL, we can save some typing by adding the following to build.sbt:

initialCommands in console := """import com.eed3si9n.tetrix._
|import Stage._""".stripMargin,

After reloading, type in console from sbt shell and open the REPL:

[info]
import com.eed3si9n.tetrix._
import Stage._
Welcome to Scala version 2.10.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_51).
Type in expressions to have them evaluated.

scala> move // hit tab key
moveLeft    moveRight

Yes, the tab key completion works in the REPL.

scala>     val s = newState(Seq((1, 0), (1, 1), (2, 1), (2, 2))
map { Block(_, ZKind) }, (10, 20), TKind :: TKind :: Nil)
s: com.eed3si9n.tetrix.GameState = GameState(List(Block((1,0),ZKind), Block((1,1),ZKind),
Block((2,1),ZKind), Block((2,2),ZKind), Block((4,18),TKind), Block((5,18),TKind),
Block((6,18),TKind), Block((5,19),TKind)),(10,20),
Piece((5.0,18.0),TKind,List((-1.0,0.0), (0.0,0.0), (1.0,0.0), (0.0,1.0))),
Piece((2.0,1.0),TKind,List((-1.0,0.0), (0.0,0.0), (1.0,0.0), (0.0,1.0))),List(),ActiveStatus,0)

scala>     val heights = s.unload(s.currentPiece).blocks map {
_.pos} groupBy {_._1} map { case (k, v) => (k, v.map({_._2}).max) }
heights: scala.collection.immutable.Map[Int,Int] = Map(1 -> 1, 2 -> 2)

scala>     val gaps = (0 to s.gridSize._1 - 2).toSeq map { x =>
heights.getOrElse(x, 0) - heights.getOrElse(x + 1, 0) } filter {_ > 1}
gaps: scala.collection.immutable.IndexedSeq[Int] = Vector(2)

Off by one error! Did you catch this? The lowest coordinate is 0, yet I am returning 0 as the default.

Also I am throwing out the negative numbers. The correct gap should be:

scala>     val gaps = (0 to s.gridSize._1 - 2).toSeq map { x =>
heights.getOrElse(x, -1) - heights.getOrElse(x + 1, -1) } filter {math.abs(_) > 1}
gaps: scala.collection.immutable.IndexedSeq[Int] = Vector(-2, 3)

I didn’t catch this because my hand calculated value of -36.0 was also incorrect, which should have been -49.0. Now all tests pass:

[info] + penalize having gaps between the columns

It feels more logical now, but the penalty isn’t nudging the game to actual scoring or creating the right set up. First, I want to separate the reward component and penalty component of the utility function so it’s easier to test. Second, instead of the gaps, let’s try penalizing the heights in general.

s2"""
Penalty function should
penalize having blocks stacked up high                                    \$penalty1
"""
...
def penalty1 = {
val s = newState(Seq(
(0, 0), (0, 1), (0, 2), (0, 3), (0, 4), (0, 5), (0, 6))
map { Block(_, TKind) }, (10, 20), TKind :: TKind :: Nil)
agent.penalty(s) must_== 49.0
} and {
val s = newState(Seq((1, 0))
map { Block(_, ZKind) }, (10, 20), TKind :: TKind :: Nil)
agent.penalty(s) must_== 1.0
}

Here’s the new penalty:

def penalty(s: GameState): Double = {
val heights = s.unload(s.currentPiece).blocks map {
_.pos} groupBy {_._1} map { case (k, v) => v.map({_._2 + 1}).max }
heights map { x => x * x } sum
}

Another thing I want to tweak is the balance between the reward and penalty. Currently the incentive of deleting the line is too little compared to avoiding the penalty.

def utility(state: GameState): Double =
if (state.status == GameOver) minUtility
else reward(state) - penalty(state) / 10.0

This at least made the agent delete a line in the following game: