# Logarithm in Exam

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Logarithm in Exam
Hey,

how are we supposed to calculate the logarithm of 2 in the exam without a calculator?
Sorry to be so blunt but I don’t see any didactic value in learning the logarithmic values (for nontrivial arguments)

Thanks

You DON’T. I’m pretty sure I mentioned repeatedly that you’re not supposed to compute ANYthing in the exam.

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I am delighted to be equally blunt: neither do I; except for the two facts log_2(1024)=10 and log_2(x*y)= log_2(x)+log_2(y), that anyone dabbling in CS should know and which empower you to calculate
log_2(41034256) ~ log_2(4) + log_2(1024) + log_2(1024) = 2 + 10 + 10 = 22.

But I doubt that even this will be necessary in the exam. What we are after is concepts not calculation.

Sorry to keep this thread alive.

But looking at the old exams the creation of a decision tree requires the calculation of the information gain and with that the logarithm. And not the simple forms that Prof. Kohlhase mentioned in the post before.

Is there any trick to apply to come up with the result without a concrete computation?
Sorry if this is a stupid question but I really do not the answer to the question.

In the exercise it’s said “apply the decision tree learning algorithm” which in my opinion means “write down the formulas and name the splitting criterion”. It never mentions “compute the values”. Hope this clarifies your question.

Ah okay I get it thanks!
Thought we had to lay out the complete tree. Thanks for the clarification!

If there are calculations in the “solution” I automatically think that this is required to do as well.
Also the wording “Apply the algorithm” is really misleading at least to me.

I never heard “no calculations required” before. Does this apply to every problem?

I’m also still confused, because the decision tree tasks seem to be the ones with the most points (20) and

feels not sufficient. Is this really enough?

NO. COMPUTATIONS. REQUIRED. Why are you hunting for clues that might suggest otherwise if I repeatedly told you that you won’t need to compute anything?

20 points = 10 minutes in that exam. Yes, maybe that was a bit much, but to (in 10 minutes) explain information gain and how it is computed (relative to the current point in the tree) is not something you just write down in 3 minutes without being really good at explaining yourself.

Is that „applying“ an algorithm?

Students last year were told to guess/estimate the information gains they needed. What I wanted to see and was interested in is whether they would plug in the correct proportions of table rows in the iteration steps, because that’s where people tend to fuck up, when they don’t quite understand the algorithm and only memorized equations blindly.

I should not have given you solutions…

So to alleviate your fears: Yes, students were supposed to construct an actual tree last year. No, they were not supposed to calculate anything. If numbers were involved, they were allowed to blindly guess.

If you’re confused by anything during the exam please ask. We’ll be there (actually, I won’t, but others will), and we’ll happily answer if anything is unclear.

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Wird schon schief gehen!
Ich will ja nur mal für alle anderen anmerken, dass hier niemand in die Pfanne gehauen wird. Wenn man keine Logarithmen berechnen muss, kann man auch nicht Sauer sein (was der Lehrstuhl ja auch nicht sein wird), wenn man anhand des Logarithmus normalerweise das weitere Vorgehen entscheidet und somit halt nur schätzt, da wird einem niemand einen Strick draus drehen!

Wir sind ja daran interessiert Euch gute Noten zu geben.