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Questions tagged [parallel-computing]

Questions about algorithms or programs that compute on multiple processing units simultaneously. Not to be confused with concurrent or distributed computing!

Common category tags are but also if the question is about parallel complexity (buzzwords include e.g. PRAM or NC).

Find a general introduction on fitting topics on Wikipedia.

In particular, contrast with and which have different focus. See these discussions for more information on this:

That said, if you run into issues in your parallel algorithm, certainly use this tag in addition!

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Best problems that are prone to parallelization?

What are some problems that are prone to parallelization? When I think about this, the first thing that comes to my mind is matrix multiplication, which yields to faster calculations, meaning you can get speed ups easily. Any other examples like…
user9201
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How to "convert" nested loops into code taking advantage of parallel computing?

Let's say that an algorithm uses several nested loops to accomplish it's task, for instance : An algorithm treating voxels on several frames, so there would be four dimensions : t (for time), x, y and z. An algorithm evaluating a function that…
Pop Flamingo
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Is it possible to implement 64-bit cmpxchg from 32-bit cmpxchg?

Question Given a 32-bit cmpxchg operation as a primitive: u32 cmpxchg32(u32* mem, u32 key, u32 old, u32 neo) { // this function runs atomically u32 found = mem[key]; if (found == old) { mem[key] = neo; } return…
MaiaVictor
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Why weak scaling is easier to achieve than strong scaling?

When we parallelize tasks and measure the perforamnce,two common measures of parallel scaling are Strong Scaling: Time for fixed problem size as number of processor is increased Weak Scaling: Time for fixed computational work per processor as…
syko
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Is automatic multicore support at the hardware or compiler level possible?

Due to technical constraints, single thread performance has been increasing more slowly and adding cores has been adopted to offer greater potential increase in performance. However, multicore support currently appears to require the programmer to…
Bassinator
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Why is the sequence, "1,3,2,4", not a bitonic sequence?

A Bitonic Sequence is a sequence of numbers which is first strictly increasing then after a point strictly decreasing. According to the definition of a bitonic sequence, we know that a graph of a bitonic sequence can have at most one "peak" and one…
user40628
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Good motivation for parallel data structures and algorithms

I have a more general question for you. I'm working in Parallel Data Structures and Parallel Algorithms. That is a nice topic with a lot of interesting challenges. However, I have some problem to argue for why is necessary use parallel solutions.…
José Fuentes
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Why do Amdahl's law and Gustafson's law give us different speedups, when applied on the same task?

I am given a task, where exactly 50% of the work is parallelizable. When applying Amdahl's law to calculate speedup when using 2 processing units instead of one, I get a different result than the one I get when calculating the same speedup using…
Baksel
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how can i find the Maximum Degree of Concurrency?

i'm studying Parallel Processing , and i'm confused how can i calculate the max number of concurrency in a given dependency graph ? i know that the maximum number of concurrency is the largest number of concurrent tasks at any point of the…
maher
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Running algorithms in parallel

I'm doing a course in Computational Number Theory and am currently looking at algorithms such as Euclid's algorithm, Square-roots modulo a prime, LLL reduction algorithm, McKee's method, Pollard's $p-1$ method, the elliptic curve method and a couple…
Haikal Yeo
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Analyze Speed Up in A Dispatcher-Woker Model

In a Dispatcher-Worker model of parallel computation, we have $N$ worker machines simultaneously working on the task (for example, computing the checksum of network packets). There is no synchronization between these workers. A dispatcher…
Strin
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Why bisection width of star connected network is 1?

This may seem like a simple question, but I can neither find the answer on the internet nor AI tools can give a proper answer. I was reading a book about static networks and I saw that the bisection width of the star topology is 1, but it didn't…
user164631
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Give a parallel algorithm that finds the minimal element of an unsorted array

I need to give a parallel algorithm which finds the minimal element of an unsorted array. Moreover, I need to show that $T_1 = Θ(n)$ and $T_∞ = Θ(\log n)$. As I read $Θ(\log n)$, I thought about some sort of divide and conquer algorithm, like…
RedYoel
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Parallized algorithm for getting the frequencies of numbers in an array

I have an array $A$ of length $n$, containing integers between $0$ and $n-1$ inclusively. I would like to convert this to an array of frequencies $F$, that is, $F[i]$ should be the number of times $i$ appears in the array $A$. For example,…
Mathew
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Is this an example of parallelization?

Not sure if this is the right exchange for this question. But you could definitely answer it. Note professor said this was “wrong” on their quiz. Question: Identify a daily activity that can be speed up with parallelization. My answer: People…
visc
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