Development History

3.1.1 First Version Created on May 2008

The first version of ERICA was created in May 2008, based on implementing MOGO’s famous “UCT paper” (Gelly et al., 2006). The work was motivated by the impressive performance of CRAZY STONE and MOGO in the 9×9 competition at the 2007 Computer Olympiad.

This earliest version of ERICA was written in pure C programming language. The speed was about 20,000 uniform random simulations per second on a single-core CPU of 2.26 GHz, on the 9×9 board. A board is realized by a single array, keeping the related information of a position, such as each string’s color, liberty, owner⁸ and size.

8 The owner of a string is the representative stone of it.

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MOGO-type, fixed-sequence simulation and RAVE form the basic MCTS framework of the program. In this period, the personal communications with Yizao Wang, one of the creators of MOGO, helped considerably for the author’s understanding of the “UCT paper” and to make ERICA stronger.

In the Computational Intelligence Forum & World 9 × 9 Computer Go Championship held on September 25-27, 2008, in Taiwan, ERICA ended up in the 4th position. Table 3.1 shows the result of this competition. In this tournament, ERICA

won a game against GO INTELLECT but lost to JIMMY, the strongest Taiwanese Go-playing program at that time.

Position Program Wins Country

1 MOGO 10 France Championship held on September 25-27, 2008, in Tainan, Taiwan.

In the 9×9 Go tournament at the 2008 Computer Olympiad held on September 28 to October 5, 2008, in Beijing, China, ERICA finished in 11th place among the 18 participants. Figure 3.1 shows the game between ERICA (White) andAYA (Black) in round 2. In this game, thanks to the correct handling of seki in the playout, ERICA

reversed the bad situation and won.

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Figure 3.1: The final position of the match in round 2 in the 9×9 Go tournament at the 2008 Computer Olympiad: ERICA (White) vs. AYA (Black). The stone marked by ∆ is the last move.

The groups marked by ○ form a seki. White won by resignation.

At the 2009 Computer Olympiad held on May 10-18, 2009, in Pamplona, Spain, ERICA participated in the 9×9 Go tournament with the same version that played in the previous year. Finally, ERICA scored the 6th position among the 9 participants.

3.1.2 Second Version Created on June 2009

In June 2009, a new version of ERICA was created, under the supervision of Rémi Coulom. The main advancement in this new version consists in the implementation of the Boltzmann softmax playout policy that was successful in Coulom’s CRAZY STONE. In addition to RAVE, prior information was taken into account in the formulation of progressive bias (Chaslot et al., 2007). The supervised learning algorithm Minorization-Maximization (MM) (Coulom, 2007) was used to train the pattern weights.

At the 2009 TAAI Computer Go Tournament held on October 30-31, 2009, in Taiwan, ERICA won the 3rd and 2nd position in the 9×9 Go (Table 3.2) and 19×19 Go (Table 3.3) tournaments respectively.

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Position Program Country

1 ZEN Japan

2 MOGO France

3 ERICA Taiwan

Table 3.2: The result of the 9×9 Go tournament at the 2009 TAAI Go Tournament.

Position Program Country

1 ZEN Japan

2 ERICA Taiwan

3 DRAGON Taiwan

Table 3.3: The result of the 19×19 Go tournament at the 2009 TAAI Go Tournament.

In the next month, ERICA participated in the 3rd UEC Cup held on November 28-29, 2009, in Japan, and at last scored the 6th position. In the round 2 of this tournament, ERICA for the first time defeated the well-known strong 19 × 19 Go-playing program AYA, as shown in Figure 3.2. The last move is marked by ∆. In this game, ERICA (Black) killed several White’s groups, marked by ×, and acclaimed a great victory.

Figure 3.2: The final position of the match in round 2 of the 3rd UEC Cup: ERICA (White) vs.

38 AYA (Black).. Black won by resignation.

3.1.3 Third Version Created on February 2010

In February 2010, Łukasz Lew, the author of LIBEGO was a great help in speed optimization of ERICA. The author re-wrote many primary data structures and created a new version of ERICA, under the supervision of Coulom. For instance, macros, a sort of preprocessor in C programming language, were used extensively for loop unrolling.

The speed of the simulation was accelerated by a factor of 2 compared to the previous version. In this period, we concentrated on 19×19 Go, trying hard to make use of larger patterns in the tree and improve the quality of the playout.

At the 2010 Computer Olypmiad held on September 24 to October 2, 2010, in Kanazawa, Japan, ERICA won the gold and silver medals in the 19×19 Go (Fotland, 2010) and 9×9 Go tournaments respectively. In the 19×19 Go tournament, after the final round is finished, three programs, ZEN, THE MANY FACES OF GO and ERICA were in a tie. The final positions were decided in the second playoff, when both ZEN and ERICA defeated THE MANY FACES OF GO and ERICA defeated ZEN. This indicates that the three programs were competitive in playing strength. Figure 3.3 shows the final match between ZEN (White) and ERICA (Black). This game was decided by a large-scale semeai in the opening stage. ZEN misread the semeai so that ERICA killed White’s big group (marked by ×) and secured the lead until the end.

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Figure 3.3: A position of the final match in the playoff of the 19×19 Go tournament at the 2010 Computer Olympiad: ZEN (White) vs. ERICA (Black). The previous move is marked by

∆. Black won by resignation.

In the 4th UEC Cup, held on 27th to 28th November 2010 in Japan, ERICA won the 3rd position⁹. Table 3.4 shows the result of this interesting tournament. In this tournament, the games between the strong programs clearly indicated that handling semeai correctly is particularly crucial. Figure 3.4 shows the position of the match between THE MANY FACES OF GO (White) and ERICA (Black) in round 4 of the preliminaries in the first day. This game was decided by the large-scale semeai in the middle game. The Black’s group, marked by ○, has 4 liberties A, B, C and D while the White’s group, marked by ×, has only 3 liberties E, F and G. Finally, ERICA played correctly to win this capturing race and defeated the tough rival THE MANY FACES OF

GO.

9 Special thanks to Professor Tsan-Sheng Hsu, Research Fellow of Academia Sinica, Taiwan, who kindly provided us the hardware resources, an 8-core server with 64GB memory, for this tournament.

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Position Program Country

1 FUEGO Canada

2 ZEN France

3 ERICA Taiwan

4 AYA Japan

5 THE MANY FACES OF GO America

6 COLDMILK Taiwan

7 CAREN Japan

8 PERSTONE Japan

Table 3.4: The result of the 4th UEC Cup, 2010.

Figure 3.4: A position of the match in the 4th UEC Cup: THE MANY FACES OF GO (White) vs.

ERICA (Black). The previous move is marked by ∆. Black won by resignation.