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# Questions tagged [performance]

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2answers
85 views

### Fast computing of a matrix power for large integer values in C++

I'm working with squared matrices that can be quite large, for instance, a M = 50 x 50 matrix. My objective is to compute the power of the squared matrix ...
0answers
50 views

### How to detect when to use radix sort in runtime

I'm implementing a stable integer sorting algorithm, I've chosen radix sort. I've tested LSD vs MSD implementation, wrote MSD/LSD hybrid implementation to reduce bandwidth pressure. The repo is here: ...
0answers
42 views

### The correct way to calculate the performance of my approximate algorithm

I've got a question about how best to classify the performance of an approximate algorithm. I'm trying to find the 'correct' value of a graph problem instance whose cost function has an objective ...
1answer
16 views

### Analyzing parallel performance question

I was reviewing for my CS class and came across this question and answer combo that didn't have any explanation why it was correct. I'm confused on how they got the answer: We have a system to which ...
1answer
54 views

### Interesting Speedup & Amdahl's law problem

I have found a problem on my Computer Architecture textbook which I have some issues with: We have a process which spends its time in the following way: 50% of the time, it executes common ...
1answer
155 views

### Metrics on which Clock Cycles Per Instruction(CPI) depends

In the book - Computer Organization and Design: The Hardware/Software Interface [RISC-V Edition] by Patterson and Hennessy, CPI is defined like this: The term clock cycles per instruction, which is ...
1answer
24 views

### Is it possible to generate a better random number generator algorithm from an algorithm that use N computers with one that uses N+1 computers?

Is it possible to generate a better random number generator algorithm from an algorithm that use N number of computers with an algorithm that uses N+1 number of computers? I use the word computer here,...
0answers
18 views

### What is the Memory Bandwidth Usage in a Program Related to?

We can use performance counter tools to check the memory bandwidth usage while a program is running. I want to ask what is this memory bandwidth related to? What parameters are involved in memory ...
0answers
10 views

1answer
18 views

### MAC protocol with throughput of 1

Consider a MAC protocol (ALOHA, CSMA, TDMA, etc.) that, even for very high loads, always results in a throughput of 1 (normalized with respect to the channel speed). Why is that not good if the ...
1answer
66 views

### How to compute the max. speedup achievable of parallel program?

I was given the following problem to solve: Consider a system that has 128 compute units of the same type. Suppose that a program runs for 1025 time units on a single compute unit. The total amount ...
1answer
36 views

### MIPS pipeline: choosing between slowing down a stage and adding a new stage

Suppose a new, more complicated, instruction is desired for this simple pipelined MIPS processor. Suppose, also, it could be implemented by either (a) adding new logic to the execute stage of the ...
1answer
45 views

### Help with performance and speed-up question related to number of cores and their areas

There is a question in my exam that said: Consider the following three processors (x, y, and z) that are all of varying areas. Assume that the single-thread performance of a core increases with the ...
1answer
85 views

### Doubt on Performance Comparison of Splay Trees

I'm trying to understand splay tree performance compared to a standard balanced tree like AVL/red-black. In practice, I am pretty skeptical of the amortized bounds Tarjan and Sleator proves in their ...
1answer
946 views

### Average access time in two level cache system

In a two-level cache system, the level one cache has a hit time of 1 ns (inside the CPU), hit rate of 90%, and a miss penalty of 20 ns. The level two cache has a hit rate of 95% and a miss penalty of ...
2answers
1k views

### What's an efficient algorithm to calculate line breaks (word wrap) for balanced widths (minimum raggedness)?

This is a real-world application, not a student assignment. Suppose we have some numbered boxes which are to be laid out, in order, from left to right, top to bottom, with no space between them, into ...
2answers
33 views

### Time efficient way to implement Multi-Armed-Bandits?

I'm doing a research on Multi-Armed Bandit (MAB) problem with approx. 1 million arms. In contrast, the number of iterations is of course much larger, about 10-20 million. Most MAB-algorithms require ...
1answer
26 views

### F-measure with $\beta > 1$

Consider the F-measure $F_{\beta}$. I know that with $\beta < 1$ precision is given more importance, ending with $F_{0} = precision$. With $\beta > 1$ means recall gets the upper hand, with the ...
1answer
58 views

### Performance speedup with Amdahl's law

Consider this question: A program has 1M instructions and 30% of them are SQRT with CPI=8. The CPI of the rest of the instructions are 3. If we reduce the CPI of SQRT to 2, how much speedup is ...
1answer
49 views

### Classification accuracy based on top 3 most likely classifications

My goal is to recommend jobs to job seekers based on their skill set. Currently I'm using an SVM for this, which is outputting one prediction, e.g. "software engineer at Microsoft". However, consider ...
1answer
33 views

### Simplification of a multi-index Boolean expression towards computation in fewer steps

Let $x_{ij} \in \{0,1\}$, $1 \leq i \leq M$ (typically, $M = 2000$), $1 \leq j \leq N$ (typically, $N = 10$), be Boolean variables. If possible at all, I would like to simplify the following ...
2answers
60 views

### Minimum words in a string given a dictionary

The question is: Given a dictionary consisting of a set of words and a string: find the minimum number of words the string can be split into. If the string can not be decomposed into a list of words ...
1answer
287 views

### How to prove the performance, Big Omega ,of building a binary heap using recursive method is Ω(nlog(n))

We can learn the big-O of building a binary heap using recursive method is O(n log n) from wiki "This approach, called Williams’ method after the inventor of binary heaps, is easily seen to run in O(n ...
1answer
53 views

### Slowdown when accessing data at page boundaries?

Hi I have a program which accesses memory words that are located X bytes apart in virtual address space. For instance, ...
2answers
31 views

### How to properly compare performance of a prototype against a baseline

Assume that we have a baseline software B and a new prototype P that I want to compare with B. Ideally, I want to show that P performs some orders of magnitude or X times faster than B (on average). ...
2answers
2k views

### Confusion in speed up calculation for pipeline architecture

This is an online question I am trying to solve. You are given a non-pipelined processor design which has a cycle time of 10ns and average CPI of 1.4.If a pipelined processor having 5 stages are 1ns, ...
0answers
32 views

### Can graph execution be better optimized than imperative programs?

I've been reading about Google's TensorFlow, and the way it represents calculations with graphs that are then executed by an engine. While the concept is interesting, I would like to understand why ...
2answers
585 views

### Importance of Frequency vs CAS Latency in memory performance

I was looking at the Wikipedia page for CAS Latency: https://en.wikipedia.org/wiki/CAS_latency And I noticed the obvious trend - at higher frequency, despite CAS latency degrading (growing), the ...
1answer
124 views

### Looking for algorithm to iterate over matrix

I have such a product example: ...
1answer
152 views

### Performance of Modified Dijkstra's algorithm with Binariy heap as Priority Queue

we know the performance of Dijkstra's algorithm with binary heap is O(log |V |) for delete_min, O(log |V |) for insert/ decrease_key, so the overall run time is O((|V|+|E|)log|V|). Now let's modify ...
1answer
291 views

### d-ary heap implementation vs Fibonacci heap implementation Dijkstra performance comparions

Let's say that Dijkstra’s algorithm with the priority queue using a d-ary heap. if adjusting d, we can try to achieve the best runtimes for the algorithm with d being $\sim |E|/|V|$. Then for a ...
0answers
46 views

1answer
2k views

### Recursive functions from O(n) complexity to O(log n)

For some recursive questions that require recursing on an input with a small piece removed (hence linear in the size of the input), can we reduce run time by recursing on two halves of the input each ...
1answer
3k views

### Is Timsort more efficient than merge sort and why?

I was just wondering, I think merge sort is more efficient but not sure if that is true. I know it's to do with the complexities but am still struggling to understand.
1answer
329 views

### Trilinear interpolation for distorted cubes?

Is there a variation of trilinear interpolation that works on a "cube" that has been distorted (by moving one or more of its corners by an arbitrary amount into an arbitrary direction)? I know that I ...