# By how many points did alphago win against Lee Se-dol?

Today, the computer program AlphaGo from Google won against the Go world champion Lee Sedol. I read that it won by resignation. If I understand correctly, it means that Lee realized he could not win and accepted his defeat without ending the game. My question is, by how many point AlphaGo would have won approximately if Lee had fought until the end?

• The last time Michael Redmond (9p) counted in the live commentary he said black (Lee Sedol) is leading on the board, i.e. without komi. That means alphago's lead was less than 7.5 points. I will update if I find a source with a more precise counting. Commented Mar 9, 2016 at 9:32
• Myungwan Kim (9p) in his live commentary estimated white's lead to 3 1/2 or 4 1/2 points. Commented Mar 9, 2016 at 10:20
• This question could be asked for all matches played.
– Kii
Commented Mar 10, 2016 at 12:15
• For the record, in go the point difference is not necessarily a good measure of the difference in strength. This seems especially true in the case of AlphaGo, whose algorithm chooses the safest path to victory. Commented Mar 10, 2016 at 16:25
• I'll even add that a close win by half a point is often more prestigious than a huge win by say twenty points.
– Kii
Commented Mar 11, 2016 at 10:55

The DeepMind channel on Youtube has a short review of each game by Michael Redmond 9P.

At the end of the summary for game 1, Michael estimates that black is slightly ahead on the board. When you factor in the 7.5 point komi, it means that the final score would have been around 5.5 in favor of AlphaGo.

Note that

AlphaGo does not attempt to maximize its points or its margin of victory. It tries to maximize its probability of winning.

[Source: wired]

• Yeah the last point is an important one. AlphaGo would prioritise a 100% chance of a 1 point win, over a 99% chance of a 5 point win. Not that that's a likely scenario Commented Mar 24, 2016 at 14:48

You can download the game record (.sgf) file from this link and use an score estimator as in the KGS Goban (free), which will give you W+2.5 (including komi) and by looking at the screen we can see that AlphaGo could easily got additional points, so perhaps 5.5 as in the previous answer is the best estimate.