Exam 2

Exam 2 is here: [PDF] [LaTeX Template]

Exam 2 is due at the beginning of class Tuesday.

• mmk2d

The provided LaTeX template does not compile correctly for me. Is anyone else experiencing this?

• Sorry, this is my bad. I forgot to embed to .cls file in the template. You can download it from here: cs3102ps.cls (just copy this file to the directory where the template file is).

• compsci2000

This might be a little late, but I have a question on the fading TM problem. When you say that the FTM symbols
on the tape fade over time: do you mean that after each step all the symbols, except the newly written one,
on the tape move one step closer to K, or just the symbol that the head is on after the write?

Additionally, when you mean K is a Natural number: do you mean 0,1,2,… or 1,2,3… ?

• Understanding the formal description of the computing model of the Fading TM should be enough to answer your first question.

For the section question, you can assume N = 1, 2, 3, .. (although it shouldn’t make any difference your answer if you interpret it to include 0 also).

• > I have a simple question on question 4 on exam 2. I think there’s a word left out on the verbal
> description of the Janus Machine. In the sentence that begins with ” On each step, the input
> symbols under both heads…..each head can a symbol on the tape…:”. I wanted to know what each
> hand can __?__ a symbol on the tape? Thank you!

Sorry, that’s a typo. It should say “each head can write a symbol on the tape”.

• On 4/13/2010 3:41 PM, Michael Chen wrote:
> Hello,
>
> Now that the test is over, I was wondering about the transition functions in problem #5. They
> didn’t quite seem to match the transition functions implied by the machine description.
> Instead of the ink being reapplied with the step counter at the current step, it always seemed
> to reapply at steps = 0. As a result, the ink is more like all-fade-at-K-steps ink rather than
> fading ink. Is there something I’m misinterpreting here?
>
> Thanks,
> Michael Chen

You’re right! The write symbols should have been (c, n_s) not (c, 0).

Sorry for the confusion. It doesn’t actually impact the answer to the questions, though. Hopefully this didn’t cause too much confusion in answering the question.

— Dave