Questions about the exercise sheets

Questions about the exercise sheets

di Daniel Weller -
Numero di risposte: 10

Hello all,

while working on the exercise sheets, two questions came up that maybe someone can help me with.

In Exercise02 Probabilistic Information Retrieval Task3:

It is not clear to me how the line Σwt is calculated, e.g. the value -0.405.

 

In Exercise03 Semantic Retrieval - Latent Semantic Analysis Task4:

How do I calculate the cos(q, d1) = 0.6325

 

Thanks a lot for your input. :)


In riposta a Daniel Weller

Re: Questions about the exercise sheets

di Alexander Salinger -
Hello Daniel,

Exercise02 Probabilistic Information Retrieval Task3:
-0,405 = ln(0,5*(4/3))
The 0,5 is from P(Dt|q,r). The (4/3) is from (N/Nt). -> N = 4 documents. Nt = 3 documents with term. Doc 3 doesn´t include the term, so Nt = 0 and you can´t calculate.
In riposta a Alexander Salinger

Re: Questions about the exercise sheets

di Philipp Treutlein -
Hello Alexander,

why is the "ln" used here instead of the "log"? Is there any reason for that? Can't find anything in the slides about using the "ln" in the Binary Independence Model.

Thanks in advance!
In riposta a Philipp Treutlein

Re: Questions about the exercise sheets

di Alexander Salinger -
Hello Philipp,
I don't know, it's just the formula.
Write in the exam in any case, which log/ln you use, then it can be taken into account.
The base of the logarithm changes the scaling, but not the relative relationship.
In riposta a Alexander Salinger

Re: Questions about the exercise sheets

di Philipp Treutlein -
Hi Alexander,

thanks for the answer!
I was just wondering if there is a reason for that since it deviated from the slides. But okay, then i'll follow your advice and denote what i used in the exam.
In riposta a Philipp Treutlein

Re: Questions about the exercise sheets

di Benedikt Ebing -

Hi Philipp,

as Alexander stated correctly, the choice of the logarithm just changes the scaling, so it doesn´t really matter which one is used. In this particular case, I assume that the solution was calculate with numpy, where "numpy.log" results in the natural logarithm.

Concerning the exam, either stick to the base given in the task or use the base from the lecture slides. When in doubt, just leave us a note which base you used.

Best,
Benedikt

In riposta a Alexander Salinger

Re: Questions about the exercise sheets

di Nicolas Wild -
Hey, alexander, consequently i don't get why for "shears" the (N/Nt) is taken the other way arround? shouldn't it be 4/2 either?
In riposta a Daniel Weller

Re: Questions about the exercise sheets

di Alexander Salinger -
Hello Daniel,

How do I calculate the cos(q, d1) = 0.6325:

cos(q,d1) = (q * d1) / (||q|| * ||d1||)

q * d1 = 0,9441 * 0,1059 + -0,4355 * 0,0557 + 0,7959 * 0,2485 + -0,5344 * 0,0443
||q|| = sqrt(0,9441²+-0,4355²+0,7959²+-0,5344²)
||d1|| = sqrt(0,1059²+0,0557²+0,2485²+0,0443²)

I hope this is clear.