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For question borderline with, or having application to, computer science. Consider also posting http://cs.stackexchange.com/ or http://cstheory.stackexchange.com/ instead of here, if appropriate.

2 votes

scott continuity, sub additivity

The two notions are equivalent if you take continuity with respect to the Scott topology (and not the one you define with the closure operators). Let $(X,\leq_X)$ and $(Y,\leq_Y)$ be dcpos. We say th …
Dominic van der Zypen's user avatar
1 vote
1 answer
81 views

Cycling through $\{0,1\}^n$ by shifting and applying a $n$-ary function

This question is motivated by Linear Feedback Shift Registers, which cycle through $\{0,1\}^n \setminus \{(0,\ldots,0)\}$ by shifting and applying a small set of XOR operations. Let $n>1$ be an intege …
Dominic van der Zypen's user avatar
2 votes
Accepted

If $f : [-a,a] \rightarrow \mathbb{IR}$ is Scott continuous, why are $f^-$ and $f^+$ measura...

First, we note that $\mathbb{IR}$ is ordered by $[a,b] \sqsubseteq [c,d]$ iff $[c,d] \subseteq [a,b]$, which makes $\mathbb{IR}$ into a domain. Now suppose $f: [-a,a]\to \mathbb{IR}$ is Scott-continuo …
Dominic van der Zypen's user avatar
1 vote

If $f : [-a,a] \rightarrow \mathbb{IR}$ is Scott continuous, why are $f^-$ and $f^+$ measura...

This answers @user3078439's question in his comment to my original answer. First, a short argument to show that if $P,Q$ are domains and $f:P\to Q$ is Scott-continuous, then $f$ is order preserving. …
Dominic van der Zypen's user avatar
3 votes
1 answer
179 views

Non-trivial parity maps in graphs

(This question actually arose in real life when dealing with status bits with mutual influence.) Let $G=(V,E)$ be a connected, simple, undirected graph with $|V| \geq 2$. For $v\in V$, let $N_G(v) = …
Dominic van der Zypen's user avatar
2 votes
1 answer
162 views

Is this cycling problem computable?

We have a group of $n$ people who must make a journey of length $d$. They are to start together, and their goal is to arrive at the destination at same time. They have a single bicycle, which they rid …
Dominic van der Zypen's user avatar
4 votes
2 answers
203 views

Hamilton cycles in $\{0,1\}^n$ with fixed Hamming distance

Let $n>1$ be an integer. For $a,b\in \{0,1\}^n$ let $d_h(a, b)$ denote the Hamming distance of $a$ and $b$. For $k\in \{1,\ldots,n-1\}$ let $H(n,k)$ be the graph on $\{0,1\}^n$ given by the edge set $ …
Dominic van der Zypen's user avatar
3 votes
0 answers
105 views

Hamiltonian path in $\{0,1\}^n$ with rotations and bit-flip in position 0

We consider any non-negative integer as an ordinal, that is $0=\emptyset$ and $n=\{0,\ldots,n-1\}$ for every positive integer. Let $\{0,1\}^n$ denote the set of $\{0,1\}$-vectors of length $n$. Define …
Dominic van der Zypen's user avatar
2 votes
0 answers
149 views

Binary operation approximating "addition" on $2^\omega$

Motivation. In computer science, addition of integers $a+b$ can be approximated by a very fast operation: $(a,b)\mapsto (a\oplus b) \oplus ((a\land b) \ll 1)$, where $\oplus$ denotes bitwise XOR, $\la …
Dominic van der Zypen's user avatar
5 votes
1 answer
226 views

Cycling through $\{0,1\}^{(2^n)}$ such that all Hamming distance appear equally frequently

Let $n\in\mathbb{N}$ be a positive integer. Let $\{0,1\}^{(2^n)}$ be the set of $0,1$-sequences of length $2^n$. For $a,b\in \{0,1\}^{(2^n)}$ let $d_h(a,b)$ be the Hamming distance between $a$ and $b$ …
Dominic van der Zypen's user avatar
2 votes
1 answer
57 views

Left-shift cycle generating maps $f:\{0,1\}^{c_0}\to\{0,1\}$ for fixed length $c_0$

This is a strengthening of an older question. Is there a positive integer $c_0$ with the following property? For every integer $n\geq c_0$ there is a function $f:\{0,1\}^{c_0}\to\{0,1\}$ such that th …
Dominic van der Zypen's user avatar
5 votes
1 answer
423 views

Is the set of generalized Fermat triples computable?

Is $\;\big\{(a,b,c)\in\mathbb{N}^3: \big(\exists m,n,\ell \in (\mathbb{N}\setminus\{0,1,2\})\big): a^m + b^n= c^\ell\big\}\;$ computable?
Dominic van der Zypen's user avatar
6 votes
1 answer
359 views

Large subgroups of Knuth's non-associative "group" on ${\cal P}(\mathbb{N})$

Donald Knuth introduced a fast, bit-wise approximation to integer addition by $$(a,b) \mapsto a \, ^{\land} \, b \, ^{\land} \, ((a \text{ & } b) \ll 1)$$ where $a,b$ are given in binary and $\,^{\lan …
Dominic van der Zypen's user avatar
13 votes
0 answers
255 views

Is the set of power matrices decidable?

Let $\text{Mat}(n\times n,\mathbb{Z})$ denote the collection of integer $n\times n$ matrices. We say $M\in \text{Mat}(n\times n,\mathbb{Z})$ is a power matrix if there is an integer $k>1$ and a matrix …
Dominic van der Zypen's user avatar
4 votes
1 answer
160 views

Is sum-balanceability computable?

Let $\mathbb{N}$ denote the set of positive integers, and let $G=(V,E)$ be a finite simple, undirected graph. Given $f:V\to \mathbb{Z}$ we define the neighborhood sum function $\mathrm{nsum}_f:V\to\ma …
Dominic van der Zypen's user avatar

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