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General information

Student:Lukáš Ondráček
Office:CoRE 407
School:Department of Theoretical Computer Science and Mathematical Logic, Charles University, Prague
Adviser:Periklis Papakonstantinou
Collaborators: Pavel Dvořák, Jakub Pekárek, Kyle Hess
Project:Time Versus Space

Project Description

We study the relation between space and time of computation of a Turing machine, which can be alternatively described in terms of depth and size of a circuit. Our current goal is to improve the result of TIME(T) ⊆ SPACE(T/log T).

Progress

1st week

Introductory presentation to the topic.
Studying time vs. space and size vs. depth relations in turing machines and circuits, respectively.

2nd week

We have figured out a way of converting multitape Turing machine into a circuit of linear depth (w.r.t. the original time), linear-logarithmic size, bounded in-degree, and other useful properties.

3rd week

We were proving correctness of our construction and discovering possible ways of compressing the depth of the circuit. A simple compression leads to the same depth as state-of-the-art constructions.

4th week

We were trying to combine two known constructions for depth compression. Unfortunately, this appeared to be a blind alley because of proving their equivalence. Finally, another possible research direction was found.

5th week

We were developing the new ideas and obtained a new construction for one-tape Turing machine. We were however not able to adjust the construction for multiple tapes, yet.

6th week

Kyle succeeded modifying the construction by adding a new but read-only tape into the Turing machine. He also partitioned the construction into multiple stages and presented it in a well-structured way. We were then trying to allow modifications of the new tape, which was not successful, yet.

7th week

We were preparing our final presentation with results and saw all the other presentations on Thursday and Friday. There was little progress during the remaining time.

8th week

Two workshops and a conference were happening that week, so there was also not much time for research. We were thinking about our constructions but no useful ideas appeared.