<p>I couldn't understand your question clearly, however, it think you are making a slim mistake. let's look at the flowing code from &quot;Russell &quot; and do pruning step by step:
<a href="https://i.sstatic.net/Fwvhe.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Fwvhe.png" alt="enter image description here" /></a>
<a href="https://i.sstatic.net/TcWDQ.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/TcWDQ.png" alt="enter image description here" /></a>
<br/>Assume your are In D and you have traversed its both children, Alpha at D becomes 20. We then return back to B, Beta becomes 20 (note that Alpha is -Inf in D). We go to E then L and then back to E. 30 is greater than Beta, so the rest is pruned. Not that Alpha remains -Inf in E, though its value here isn't important. we go back to B the value of Beta remains on changed 20. If we go to F and return back to B Beta remains unchanged and is still 20 (Note that Alpha is still -Inf). We return to A, Alpha becomes 20, And Beta remains +Inf. <br/>
So, Considering the code, the max node does not get the Alpha value from its children, rather it decides on its own by setting Alpha = max(Alpha, and returned value of its child) after visiting each child. the same is true for Beta.</p>

CC BY-SA 4.0
2021-01-06T14:47:11.290Z
2021-01-06T14:57:25.950Z
2021-01-06T14:57:25.950Z
Reza_va
<p>I want to do alpha-beta pruning on this tree:</p>
<ol>
<li><p>Consider nodes J and K. K is the max. Therefore, node D has an alpha value of 20, node B has a beta value of 20.</p>
</li>
<li><p>Move to Node E. Pass the beta value of 20 to node E. Node L has an alpha value of 30, therefore, at this point 30 (alpha) &gt; 20 (beta) and we can prune the E to M branch.</p>
</li>
<li><p>Now is my question. My original beta value at node B was 20, and the alpha value passed up to node A was 20. Then, in step 2, I changed the alpha value to be 30. Do i then change the beta value at node B to be 30, and the alpha value at node A to be 30? (and therefore pass 30 as the alpha value to node C)? Or do I keep the original value of 20 at node B, A and C?</p>
</li>
</ol>
<p><a href="https://i.sstatic.net/XpHg5.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/XpHg5.png" alt="enter image description here" /></a></p>

<minimax><alpha-beta-pruning>
Does the alpha/beta value of parent nodes change if the alpha beta value of the child node changes?
Slowat_Kela
# Does the alpha/beta value of parent nodes change if the alpha beta value of the child node changes?

(Asked by: username_0 on 2020-12-31)

I want to do alpha-beta pruning on this tree:

1. Consider nodes J and K. K is the max. Therefore, node D has an alpha value of 20, node B has a beta value of 20.
2. Move to Node E. Pass the beta value of 20 to node E. Node L has an alpha value of 30, therefore, at this point 30 (alpha) > 20 (beta) and we can prune the E to M branch.
3. Now is my question. My original beta value at node B was 20, and the alpha value passed up to node A was 20. Then, in step 2, I changed the alpha value to be 30. Do i then change the beta value at node B to be 30, and the alpha value at node A to be 30? (and therefore pass 30 as the alpha value to node C)? Or do I keep the original value of 20 at node B, A and C?

[![enter image description here](https://i.sstatic.net/XpHg5.png)](https://i.sstatic.net/XpHg5.png)

**Tags:** minimax, alpha-beta-pruning


---

## 1 answers

### Answer by username_1 on 2021-01-06. Score: 1

I couldn't understand your question clearly, however, it think you are making a slim mistake. let's look at the flowing code from "Russell " and do pruning step by step:
[![enter image description here](https://i.sstatic.net/Fwvhe.png)](https://i.sstatic.net/Fwvhe.png)
[![enter image description here](https://i.sstatic.net/TcWDQ.png)](https://i.sstatic.net/TcWDQ.png)
  
Assume your are In D and you have traversed its both children, Alpha at D becomes 20. We then return back to B, Beta becomes 20 (note that Alpha is -Inf in D). We go to E then L and then back to E. 30 is greater than Beta, so the rest is pruned. Not that Alpha remains -Inf in E, though its value here isn't important. we go back to B the value of Beta remains on changed 20. If we go to F and return back to B Beta remains unchanged and is still 20 (Note that Alpha is still -Inf). We return to A, Alpha becomes 20, And Beta remains +Inf.   
So, Considering the code, the max node does not get the Alpha value from its children, rather it decides on its own by setting Alpha = max(Alpha, and returned value of its child) after visiting each child. the same is true for Beta.


---

