Problem Detail: I have just used a function ‘rand()’ in my algorithm. In fact, it was arc4random() that I used. However, it got me thinking, how is randomness created in a computer system? Can anything ever truly be random when it Read More …
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[Solved]: definition of formula validity
Problem Detail: I read in some sources that valid formulas are tautologies (valid under every evaluation). In the others, I read that these are formulas that have conclusions true when premises are true. Are these just equivalent definitions because ⊨ P Read More …
[Solved]: Group isomorphism to graph ismorphism
Problem Detail: In reading some blogs about computational complexity (for example here)I assimilated the notion that deciding if two groups are isomorphic is easier than testing two graphs for isomorphism. For example, on the stated page it says that graph isomorphism Read More …
[Solved]: Blob detection as Constraint satisfaction problem?
Problem Detail: In image processing I have a black and white image which is represented by matrix {0,1}, I have to find blob (a region of connected pixels) in it. I’m confused, can this problem be reduced to Constraint Satisfaction problem Read More …
[Solved]: Poker with Bluffing (game theory)
Problem Detail: I’m doing a self-study of Game Theory Evolving by Gintis, and am stuck on problem 4.16 “Poker with Bluffing”. The first question asks “Show that Ollie has 64 pure strategies and Stan has 8 pure strategies.“. But no matter Read More …
[Solved]: Why is SAT in NP?
Problem Detail: I know that CNF SAT is in NP (and also NP-complete), because SAT is in NP and NP-complete. But what I don’t understand is why? Is there anyone that can explain this? Asked By : user2795095 Answered By : vzn Try Read More …
[Solved]: Is induced subgraph isomorphism easy on an infinite subclass?
Problem Detail: Is there a sequence of undirected graphs ${C_n}_{nin mathbb N}$, where each $C_n$ has exactly $n$ vertices and the problem Given $n$ and a graph $G$, is $C_n$ an induced subgraph of $G$? is known to be in class Read More …
[Solved]: Decidability of languages
Problem Detail: $L_1$ is a recursively enumerable language over some alphabet $Sigma$. An algorithm effectively enumerates its words as $w_1, w_2, …$. $L_2$ is another language over $Sigma cup {#}$ as ${w_i#w_j : w_i, w_j in L_1, i < j}$ Read More …
[Solved]: Why are lambda-abstractions the only terms that are values in the untyped lambda calculus?
Problem Detail: I am confused about the following claim: “The only values in the untyped lambda calculus are lambda-abstractions”. Why are the other terms not values? What does it mean for a lambda-abstraction to be a value? The first thing that Read More …
[Solved]: Maximal difference of height between two leaves in an AVL tree
Problem Detail: What is the maximal difference between heights of leaves in an AVL tree? I am interested only in the asymptotic difference. I am not sure about my answer – I think that it is $O(log n)$, given the fact Read More …
