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 Post subject: Kyu Exercise 109 on sensei
Post #1 Posted: Sat Dec 03, 2022 1:43 pm 
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I tried to find the solution of https://senseis.xmp.net/?KyuExercise109 exercice which is marked unresolved.
Let me reword the exercice as follows:

Click Here To Show Diagram Code
[go]$$W what is the best white move ?
$$ ------------------
$$ | . O . X . O . . .
$$ | a X b X O O . . .
$$ | . O . X O O . . .
$$ | . c X X O . . . .
$$ | X X O O O . . . .
$$ | . X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$[/go]


After several attemps my conclusion is the following:
- if black has two or more ko threats available then white shoud play at "c"
- otherwise white should play at "a".
white at "b" is not a good move.

Do you agree with this result?

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 Post subject: Re: Kyu Exercise 109 on sensei
Post #2 Posted: Sat Dec 03, 2022 2:03 pm 
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kyudan exercise?

I can't confirm, also haven't spent much time on it, but "c" looks good enough to me, "a" like black is defending with an unfavorable approach ko and "b" looks like white is also ko-killing black. I guess that is same conclusion, when being reductionist, but I wonder if I'd find faults in my own observation if I tried to make diagrams :study:

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 Post subject: Re: Kyu Exercise 109 on sensei
Post #3 Posted: Sat Dec 03, 2022 2:19 pm 
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kvasir wrote:
kyudan exercise?

I can't confirm, also haven't spent much time on it, but "c" looks good enough to me, "a" like black is defending with an unfavorable approach ko and "b" looks like white is also ko-killing black. I guess that is same conclusion, when being reductionist, but I wonder if I'd find faults in my own observation if I tried to make diagrams :study:


The problem with "c" is that black becomes unconditionnaly alive isn't it?

Click Here To Show Diagram Code
[go]$$W what is the best white move ?
$$ ------------------
$$ | . O . X . O . . .
$$ | 2 X . X O O . . .
$$ | . O . X O O . . .
$$ | . 1 X X O . . . .
$$ | X X O O O . . . .
$$ | . X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$[/go]

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 Post subject: Re: Kyu Exercise 109 on sensei
Post #4 Posted: Sat Dec 03, 2022 2:50 pm 
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Yes but it is W+3 and sente. So I called it "good enough".

Click Here To Show Diagram Code
[go]$$Wm3
$$ ------------------
$$ | . O 4 X . O . . .
$$ | X X . X O O . . .
$$ | . O 2 X O O . . .
$$ | 3 O X X O . . . .
$$ | X X O O O . . . .
$$ | 1 X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$[/go]


and this is at minimum B+9 gote, so we can call "c" at least 12 point move?
Click Here To Show Diagram Code
[go]$$Bm1
$$ ------------------
$$ | . O . X . O . . .
$$ | 2 X 3 X O O . . .
$$ | 1 O . X O O . . .
$$ | 4 5 X X O . . . .
$$ | X X O O O . . . .
$$ | . X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$[/go]



Btw the following seems to fail for black but now I'm making diagrams :study:
Click Here To Show Diagram Code
[go]$$Bm1
$$ ------------------
$$ | . O . X . O . . .
$$ | 2 X 3 X O O . . .
$$ | 4 O . X O O . . .
$$ | . 1 X X O . . . .
$$ | X X O O O . . . .
$$ | . X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$[/go]

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 Post subject: Re: Kyu Exercise 109 on sensei
Post #5 Posted: Sat Dec 03, 2022 4:19 pm 
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I agree with count kvasir but did you count also a white move at "a"?

Click Here To Show Diagram Code
[go]$$W what is the best white move ?
$$ ------------------
$$ | . O . X . O . . .
$$ | 1 X . X O O . . .
$$ | . O . X O O . . .
$$ | . . X X O . . . .
$$ | X X O O O . . . .
$$ | . X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$[/go]


Without black ko threats (or at most one ko threat) black seems dead and white gains 27 points in the corner.
Comparing to the 9 black points when black plays first that means that the value of white "a" is 36 points gote (deiri count).
For that reason I prefer "c" ONLY if black has at least two ko threats available.

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 Post subject: Re: Kyu Exercise 109 on sensei
Post #6 Posted: Sat Dec 03, 2022 5:37 pm 
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How interesting :)

No I didn't count it, I used my intuition and claimed "c" was "good enough".

I see it slightly differently from you but I am not confident I see the right ko so bare with me.

Now I see white starting a ko like this, not sure it is the same as what I thought I saw before but this is not a real approach ko (maybe I hallucinated or I don't see the right ko?). It is W+14 because it is the value of a move in the ko is 12 pts. and white will be one move from finishing the ko for W+26 (and for that matter black finishing the ko is B+10).

Click Here To Show Diagram Code
[go]$$W
$$ ------------------
$$ | . O 8 X 7 O . . .
$$ | 1 5 3 X O O . . .
$$ | 4 O 6 X O O . . .
$$ | 9 2 X X O . . . .
$$ | X X O O O . . . .
$$ | . X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$[/go]


So we have W+14 in gote or B+9 in gote from the following position, assuming white plays "a". That is the move is 11.5 pts. which is actually less than the 12 pts move when assuming black plays "c". Therefore, you can play "c" because it is "good enough" or play "a" going -0.5 pts. for the exchange which could favor white because the 12 pts. per move could be heavy. Also white might tenuki for a less favorable ko and that is another exchange.

Basically, by this count it looks like "c" is only better if the ko is heavy for black. That is, if it is difficult for black to find sufficient ko threats then the "c" is better and this could be the case when each move in the ko is 12 pts. but it is not a given. I don't think this has much to do with the number of threats, rather the quality of threats.

Click Here To Show Diagram Code
[go]$$W
$$ ------------------
$$ | . O . X . O . . .
$$ | a X b X O O . . .
$$ | . O . X O O . . .
$$ | . c X X O . . . .
$$ | X X O O O . . . .
$$ | . X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$[/go]


Anyway, I might have made mistakes :study: It is not true of every possible whole board positions but I am inclined in general to just be happy to have a "good enough" move that I can be reasonably sure isn't nonsense. You could add stones to the black group to make the ko clearly favored in terms of the above analysis.

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 Post subject: Re: Kyu Exercise 109 on sensei
Post #7 Posted: Sun Dec 04, 2022 7:17 am 
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kvasir wrote:
Now I see white starting a ko like this

Click Here To Show Diagram Code
[go]$$W
$$ ------------------
$$ | . O 8 X 7 O . . .
$$ | 1 5 3 X O O . . .
$$ | 4 O 6 X O O . . .
$$ | 9 2 X X O . . . .
$$ | X X O O O . . . .
$$ | . X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$[/go]



Yes kvasir this is a ko but I do not think it is the best sequence for white point of view because in this sequence Black needs only one ko threat to win the ko (surely this is not a kyu level exercice!).

What about this other sequence:

Click Here To Show Diagram Code
[go]$$W
$$ ------------------
$$ | . O . X 5 O . . .
$$ | 1 . 3 X O O . . .
$$ | 4 O 6 X O O . . .
$$ | 7 2 X X O . . . .
$$ | X X O O O . . . .
$$ | . X O . . . . . .
$$ | O O O . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$[/go]


kvasir wrote:
It is W+14 because it is the value of a move in the ko is 12 pts. and white will be one move from finishing the ko for W+26 (and for that matter black finishing the ko is B+10).

So we have W+14 in gote or B+9 in gote from the following position, assuming white plays "a". That is the move is 11.5 pts. which is actually less than the 12 pts move when assuming black plays "c". Therefore, you can play "c" because it is "good enough" or play "a" going -0.5 pts. for the exchange which could favor white because the 12 pts. per move could be heavy. Also white might tenuki for a less favorable ko and that is another exchange.


If I am not wrong you applied the rule of thumb described in https://senseis.xmp.net/?KoThreatRuleOfThumb

In principle I agree with your count but you know also that this rule of thumb cannot be applied to big ko (compared to the ambient temperature).

In the same article you find the following warning:

"The books, e.g. Rob van Zeijst's All About Ko, tell you to compare the ko with the threat, 2K/3 vs. H. That is not very good advice, unfortunately.
Note that the values of your own threats, as well as the value of other plays on the board, are relevant. In particular, you can afford to reply to a small threat of the opponent if your corresponding threat is large enough. :)
This formula works when you make two key simplifying assumptions:
The ko is only fought when the ko is the same size as the ambient temperature (miai values are equal: K/3 = T). This will be true for many kos, because if the ko is smaller than the ambient temperature, players will simply ignore it until the temperature drops to the same value as the ko, and only at that moment fight the ko. However, sometimes a ko arises from local fighting, and the size of the ko is larger than the ambient temperature (K/3 > T).
They ignore the size of the threats that you still have in reserve. (TODO: Add some discussion about why ignoring the threats you have in reserve is bad)"

When I analysed the proposed position and I discovered the ko I immediately considered it is probably a ko too big for the rule of thumb.
Let's take a typical example :

Click Here To Show Diagram Code
[go]$$W
$$ -------------------------
$$ | . O . X . O X X X X X |
$$ | a X . X O O X X X X X |
$$ | . O . X O O O O O O g |
$$ | . c X X O X X X X X X |
$$ | X X O O O X . O O O O |
$$ | . X O . O X X . O O . |
$$ | O O O O . O X O O O X |
$$ | . O . k O O X . O O . |
$$ | O O . X O X X O O O O |
$$ | . O . X O X . X X X X |
$$ | O O . X O X . . . . . |
$$ -------------------------
$$[/go]


It seems white "c" is a good choice for two reasons :
1) taking sente in the upper left corner allows to take the big yose at "g"
2) black has a big ko threat at "k".

Even in this case the best move is white "a" because white is able to win ko

kvasir wrote:
You could add stones to the black group to make the ko clearly favored in terms of the above analysis.


I can only agree kvasir but the ko is already a very large ko, isn't it?

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 Post subject: Re: Kyu Exercise 109 on sensei
Post #8 Posted: Sun Dec 04, 2022 11:03 am 
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Gérard TAILLE wrote:
What about this other sequence:


This looks like it could be a better ko. Hopefully this was the ko I saw originally, not so sure about that though. However, the move in this ko is less than the other ko. In this case winning the ko is W+25 or B+10 and there are 4 steps, the value per move is 8.75 pts. (less than the 12 pts. for the other one) and this gives the position a W+15.25 value (not much more than the W+14 for the other ko). In this case the move is 13.125 12.125 pts. in the position before and that is more than the 11.5 pts. with the other ko and the 12 pts. for "c". Really it is not that much for someone that might not see the right ko or play a bad ko threat :)

Gérard TAILLE wrote:
In principle I agree with your count but you know also that this rule of thumb cannot be applied to big ko (compared to the ambient temperature).


There will be an exchange and it can favor either side. If the players reach this position while perfectly matching each other's moves then it is actually white that has the larger stake in the ko and stands to lose more if there aren't sufficient ko threats. If the player instead reach the position in a way that has black playing lower value moves elsewhere then it is still white that has a large stake in the ko and black's slow play is sunk cost that will be reflected in the overall positional judgment instead of the local position.

Gérard TAILLE wrote:
When I analysed the proposed position and I discovered the ko I immediately considered it is probably a ko too big for the rule of thumb.


There are multiple kos that are possible, they have different move value and different position value. If you can see clearly that the ko is too big then you can force the exchange and gain the difference between the move in the ko and the ko threat. If you can't see it clearly then you can have lose the difference between the ko and the ko threat.

Gérard TAILLE wrote:
Let's take a typical example :

It seems white "c" is a good choice for two reasons :
1) taking sente in the upper left corner allows to take the big yose at "g"
2) black has a big ko threat at "k".

Even in this case the best move is white "a" because white is able to win ko


I am really not sure. I'd just have to lay out the diagrams and asses it like that. That approach ignores that I might not see clearly what kos could be played how they would be played, the error introduced by that is not insignificant. I called "c" good enough, I don't think this complicated analysis changes my mind.

The following could be wrong in different ways but maybe illustrates that it is pretty difficult.
Click Here To Show Diagram Code
[go]$$W B+3
$$ -------------------------
$$ | . O 6 X . O X X X X X |
$$ | 2 X . X O O X X X X X |
$$ | . O 4 X O O O O O O 7 |
$$ | 5 1 X X O X X X X X X |
$$ | X X O O O X . O O O O |
$$ | 3 X O . O X X . O O . |
$$ | O O O O . O X O O O X |
$$ | . O . . O O X . O O . |
$$ | O O . X O X X O O O O |
$$ | . O . X O X . X X X X |
$$ | O O . X O X . . . . . |
$$ -------------------------
$$[/go]


Click Here To Show Diagram Code
[go]$$W B+16?
$$ -------------------------
$$ | . O 8 X . O X X X X X |
$$ | 1 X 3 X O O X X X X X |
$$ | 4 O 6 X O O O O O O 5 |
$$ | 7 2 X X O X X X X X X |
$$ | X X O O O X . O O O O |
$$ | . X O . O X X . O O . |
$$ | O O O O . O X O O O X |
$$ | . O . . O O X . O O . |
$$ | O O . X O X X O O O O |
$$ | . O . X O X . X X X X |
$$ | O O . X O X . . . . . |
$$ -------------------------
$$[/go]


Click Here To Show Diagram Code
[go]$$W B+16?
$$ -------------------------
$$ | . O 7 X . O X X X X X |
$$ | 1 X 3 X O O X X X X X |
$$ | 4 O 6 X O O O O O O . |
$$ | 5 2 X X O X X X X X X |
$$ | X X O O O X . O O O O |
$$ | . X O . O X X . O O . |
$$ | O O O O . O X O O O X |
$$ | . O . . O O X . O O . |
$$ | O O . X O X X O O O O |
$$ | . O . X O X . X X X X |
$$ | O O . X O X . . . . . |
$$ -------------------------
$$[/go]


Click Here To Show Diagram Code
[go]$$W is this where black is out of threats? but it is b+4?
$$ -------------------------
$$ | . O 8 X 7 O X X X X X |
$$ | 1 5 3 X O O X X X X X |
$$ | 4 O 6 X O O O O O O . |
$$ | 9 2 X X O X X X X X X |
$$ | X X O O O X . O O O O |
$$ | . X O . O X X . O O . |
$$ | O O O O . O X O O O X |
$$ | . O . 0 O O X . O O . |
$$ | O O . X O X X O O O O |
$$ | . O . X O X . X X X X |
$$ | O O . X O X . . . . . |
$$ -------------------------
$$[/go]


Click Here To Show Diagram Code
[go]$$W or this way? but still B+4?
$$ -------------------------
$$ | . O . X 7 O X X X X X |
$$ | 1 X 3 X O O X X X X X |
$$ | 4 O 6 X O O O O O O . |
$$ | 5 2 X X O X X X X X X |
$$ | X X O O O X . O O O O |
$$ | . X O . O X X . O O . |
$$ | O O O O . O X O O O X |
$$ | . O . . O O X . O O . |
$$ | O O . X O X X O O O O |
$$ | . O . X O X . X X X X |
$$ | O O . X O X . . . . . |
$$ -------------------------
$$[/go]


You have to give me the variation :scratch:

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 Post subject: Re: Kyu Exercise 109 on sensei
Post #9 Posted: Sun Dec 04, 2022 12:04 pm 
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Here is my magic sequence:

Click Here To Show Diagram Code
[go]$$W
$$ -------------------------
$$ | . O . X 5 O X X X X X |
$$ | 1 X 3 X O O X X X X X |
$$ | 4 O 6 X O O O O O O . |
$$ | 7 2 X X O X X X X X X |
$$ | X X O O O X . O O O O |
$$ | . X O . O X X . O O . |
$$ | O O O O 9 O X O O O X |
$$ | . O . 8 O O X . O O . |
$$ | O O . X O X X O O O O |
$$ | . O . X O X . X X X X |
$$ | O O . X O X . . . . . |
$$ -------------------------
$$[/go]


Click Here To Show Diagram Code
[go]$$Bcm10
$$ -------------------------
$$ | . O . X O O X X X X X |
$$ | O 2 O X O O X X X X X |
$$ | 1 O X X O O O O O O 3 |
$$ | O X X X O X X X X X X |
$$ | X X O O O X . O O O O |
$$ | 4 X O . O X X . O O . |
$$ | O O O O O O X O O O X |
$$ | . O . X O O X . O O . |
$$ | O O . X O X X O O O O |
$$ | . O . X O X . X X X X |
$$ | O O . X O X . . . . . |
$$ -------------------------
$$[/go]


Playing :b12: at C11 do not change the result.

Assuming a komi 0.5 then white wins the game by 0.5 points.
In this example white "a" gains 3 points compare to white "c". Not bad, is it?

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 Post subject: Re: Kyu Exercise 109 on sensei
Post #10 Posted: Sun Dec 04, 2022 1:13 pm 
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Gérard TAILLE wrote:
Assuming a komi 0.5 then white wins the game by 0.5 points.
In this example white "a" gains 3 points compare to white "c". Not bad, is it?


That works out for me. Can you make a middle game example :tmbup:

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 Post subject: Re: Kyu Exercise 109 on sensei
Post #11 Posted: Sun Dec 04, 2022 3:36 pm 
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kvasir wrote:
Gérard TAILLE wrote:
Assuming a komi 0.5 then white wins the game by 0.5 points.
In this example white "a" gains 3 points compare to white "c". Not bad, is it?


That works out for me. Can you make a middle game example :tmbup:


Oops, the number of middle type positions is very high and no example can be significant.
My general view is the following.
1) as long as white can avoid to play and choose between "a" and "c" she has better to play on another part of the board. By leaving the two options open black has to face more difficulties. It is the case when the ambiant temperature is greater than 12 because 12 is the value of the sente move at "c" (reverse sente for black).
At the beginning of the game the temperature is near 14 and this temperature will certainly not drop rapidly to 12.
2) When the temperature is about equal to 9, 10 or 11 the situation may become extremely complex. Because a move at "c" is simplier to analyse a good strategy seems the following : if after "c" you estimate the position is better for you (let's say more than 50% chance for winning) then choose the "c" move otherwise chose the "a" move hoping for better chance.
3) if temperature is 8 or lower I think most of the time the "a" move will be better than "c" => except if you are quite sure to win with the simple "c" move you should choose "a" move.

My feeling is that moves "a" and "c" are quite equivalent when ambiant temperature is equal to 10. As you can see I agree with your intuition: beginning with a position in which the temperature is greater than 12 then the player will wait till temperature drops and it may often happen that the move "c" will be better than "a" when reaching temperature 11.

Note : I do not understand how this exercice can be considered a KYU exercice :scratch: :-?

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 Post subject: Re: Kyu Exercise 109 on sensei
Post #12 Posted: Mon Dec 05, 2022 6:57 am 
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Let me try to explain my feeling concerning the value 10 for the ambiant temperature.

Let's suppose an environment made of gote areas : g1 >= g2 >= g3 ... By definition the ambiant temperature is equal to g1.
Let's try now to see how the white move "a", leading to a ko, will be handled. OC we need to now the white threats and the black threats available and the corresponding analysis could be very complew in practice. For that reason I propose the following major simplification : white and black have a lot of ko threats, of different values from big one to smaller one, and in addition I assume these ko threats are about the same for white and black. With this simplification, at each step of the ko fight white and black will use ko threats about the same value and the value of ko threat will inevitably drop as the ko fight progresses.
In this context the ko will be resolved when the value of ko threat will drop to a certain value X.
Now I will calculate this value X.
If white resolve the ko then white will gain 26 points (the value of the area when white wins the ko), black will gain X points (the black ko threat) and finally white will take sente to gain g1 - g2 + g3 - g4 + ... in the environmant. Here I make another simplication : I suppose g1 - g2 + g3 - g4 + ... = g1/2
=> white white gains w1 = 26 - X + g1/2
If black resolve the ko then black will gain 10 points (the value of the area when black wins the ko), white will gain X points (the white ko threat) and finally black will take sente to gain g1 - g2 + g3 - g4 + ...
=> white gains w2 = -10 + X - g1/2
The ko will be resolved when
w1 = w2 =>
+26 - X + g1/2 = -10 + X - g1/2 =>
2X = 36 + g1 =>
X = 18 + g1/2
Now let's compre the result of move "a" with the ko and the move "c" in sente.
When white plays "c" white will gain +3 (the value of the area after the sente move "c") and white will take sente to gain g1 -g2 + g3 - g4 + ...
=> white gains w3 = +3 + g/2
move "a" and "c" will be equivalent if
w1 (= w2) = w3 =>
26 - X + g1 -g2 + g3 - g4 + ... = 3 + g1 -g2 + g3 - g4 + ... =>
X = 23
and
X = 18 + g1/2 =>
23 = 18 + g1/2 =>
g1 = 10

Under these assumptions then
1) if g1 > 12 neither white nor black should play in the concerned area
2) if not and g1 > 10 then white to move shouhd play the sente move "c" and black to move should choose the reverse sente move
3) if not then white to move shouhd play the ko move "a" and black to move should choose the reverse sente move

I perfectly know that such assumptions concerning an ideal environment or concerning the values of white and black ko threats are never reached in a given game but the goal was only to give you an idea for chosing between "a" and "c".
I hope you were interested by such analyse.

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