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Hello,

I wanted to discuss the answer key given for some of the questions in official website. The doubts are following

1) It's about alpha beta pruning (Q25 in master question paper, 1 mark). The answer should be (m) = lowest, (n) = highest (Option B) and the answer given in official key is (m) = highest, (n) = lowest (Option C).  One thing I want to note is that in the exam I have marked C as my answer which should be incorrect.

2) This is Q 59. The question is given below

The joint distrbution for two random variables X, Y is

$$f_{X,Y}(x, y) = 2xy$$ where $0<x<2$ and $0<y<x$. Find the value of $E[Y|X=1.5]$

Solving the question will give 1 (by calculating marginal distribution). The reason I have problem here is that if you observe, the distribution is not a valid distribution. That is integral of joint distrubution is not 1. Even the marginal distrubution of X which will be $f_{X}(x) = \int_{0}^{x}2xydy = x^{3}$ where $0 < x < 2$ is not a valid distrubution. When I attempted this question in the exam, then I had to double check just to see if I am doing something wrong. At the end I marked it as 1, so giving this question MAT will not effect much for me. But I wanted to post here so that I can see what other people think ?

I am planning to challenge these two questions but I feel that 2nd one will not be accepted by GATE.
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27 Comments

yes, that is not a valid joint pdf... I also have not observed it previously.
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Thank you for mentioning the issue.
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For the $\alpha-\beta$ pruning, m=highest and n=lowest is correct, why do you think it is incorrect ?
  
Apart from the joint pdf question, in data science paper, one more question is having an issue:

https://gateoverflow.in/422931/gate-ds%26ai-2024-question-31
  

Few questions from computer science paper which I have read are also having issues:

https://gateoverflow.in/422902/gate-cse-2024-set-2-ga-question-5

https://gateoverflow.in/422777/gate-cse-2024-set-1-ga-10  

Apart from these, some questions are having very small issues like $T(1)$ is having two values in a recurrence question and $G$ is a perfect matching.

There might be some more issues that people can challenge.
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@Shaik

I have not written the exam but if you want I could help you to make the draft for any question that you want to challenge..
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Okay..I would use the template of  my last year graph theory question challenge..

Would put the link here after 3-4 hours, if you want to modify then you can do it there..

What is deadline for challenging questions.. is it like 5 pm today or till 12 pm ?
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Okay,,

deadline time was not mentioned any where ,just 25 th feb they are given.
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Okay..
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edited by

The alpha beta pruning question was tricky (I felt it that way). One direct answer I can give is if you navigate to wikipedia for alpha beta pruning (https://en.wikipedia.org/wiki/Alpha%E2%80%93beta_pruning) there you can see that

```

The algorithm maintains two values, alpha and beta, which respectively represent the minimum score that the maximizing player is assured of and the maximum score that the minimizing player is assured of. Initially, alpha is negative infinity and beta is positive infinity, i.e. both players start with their worst possible score

```

Also if we think about it, lets suppose at some level $\alpha = 3$,  then we know for sure that in future $\alpha$ should be at least 3. So in turn alpha is the minimum possible value for max layer at any point (level). So if you know the definition or read this somewhere then question is easy, but figuring this out in exam was bit tricky. I took some sample values and ran the algorithm in the exam and then also at the end got it wrong.

Also what is wrong with question 31 ?. I wrote a python script for the same and it runs properly without any issues. Thing that is not mentioned is that s1 ans s2 value constraints. For example we can give the values like $s1 = -3$ and $s2 = 0$ and then also the code runs. Is there any other problem you are seeing for this question ?

I understand the ambiguity but I don't think GATE will accept the challenge (like the same way I feel for the joint probability question).

```

def fun(D, s1, s2):
if s1 < s2:
D[s1], D[s2] = D[s2], D[s1]
fun(D, s1 + 1, s2 - 1)

vf = [1, 2, 3, 4, 5]
fun(vf, 0, 3)
print(vf)

```

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Have you checked the norvig book ?

The statement is almost as it is..

Whether gate will accept or not, is a different issue but if you think then you can go the challenge if you think 1 or 2 marks are important for you.

But I don't think it is wrong..I will paste the screenshot from the norvig book soon..
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@redshellspy

can you run the python code for fun(vf,3,0)

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As I said in the case you mentioned the answer will be wrong.
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No. Didn't check the norvig book.
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@redshellspy

Check it from Norvig book: https://people.engr.tamu.edu/guni/csce421/files/AI_Russell_Norvig.pdf

Chapter 5, Page No.: 169

Theory and examples are also given there. Let me know if you have any doubt.

You have mentioned about Joint pdf question that is clearly wrong. 

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@ankitgupta.1729 

Are you done with draft for python question??

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https://www.overleaf.com/5783788945vpnzwrgmftgw#c3eda8

click on this link and make the modification as per your need and then download the pdf after clicking on arrow in the upper side.

I have added most of things. Though I have added the screenshot from jupyter notebook but I would suggest to copy and paste the python code in https://www.pythonanywhere.com/ and add the link of the output in the draft.

Let me know if you want to make any other modification.
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I am unable to see this file in editor why?

I want to change question number to 41

https://pdfhost.io/v/FsMGRN3EB_Overleaf_Example

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On opening this link https://www.overleaf.com/project/63f6f8f401bbcee68554c390

I am going to your 2023 question ,not to this year question .

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Sorry, I have put the wrong question number.

https://www.overleaf.com/9751246578cmzrmpdxsqhx#4676a6

https://pdfhost.io/v/PC6w0dIVx_Overleaf_Example

Let me know if you have any issue
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sorry galat link share ho gayi thi..
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now I am able to access ,thank you.

can we add this point ,, If we assume something and proceed then 

option d)It swaps the elements in D at indices s1 and s2, and leaves the remaining elements unchanged ,could also be answer .

for example :

list=[1,2,3,4,5,6,7]

then by fun(list,1,2) output will be [1,3,2,4,5,6,7].

It matches with both option.

so this question is ambiguous.

Is there any thing wrong in above point ?

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@ankitgupta.1729

Yes you are right. I kind of got confused but now understood that both the screenshot you have given from norvig and the statement from wikipedia is correct. The thing is with what we are comparing. For example lets assume that the initial value is $\alpha_{0}$ (iteration 0) and at any iteration $t$ is $\alpha_{t}$ and final iteration is $\alpha_{f}$.

Now we can say that $\alpha_{f} \geq \alpha_{t} \geq \alpha_{0}$. So our statements will be like this

-  $\alpha_{t} \geq \alpha_{0}$ implies that choice that we took is highest value so far (we are comparing with past)

- $\alpha_{f} \geq \alpha_{t}$ implies that choice that we took is lowest value that we can assure for max player (we are comparing with future).

In the GATE question they have asked first point. So official answer key is correct. Thanks for helping out.

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@Shaik Sohail if you make an assumption and if one option satisfies all the examples under that assumption they you can say that option is correct with respect to that assumption.

By one counter-example, we have eliminated all the given options, it means no option is satisfying that counter-example and it shows that no option is correct or you can say the given question is incorrect. 

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@ankitgupta.1729 

Okay 👍, thank you for helping. 

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Hello,

I have contested the question 59 and I feel there is very low chance that GATE accepts it as valid contest (given that they had to give lot of MAT's in Mechanical paper and its not good for any exam committee to accept that there question was wrong).
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