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Questions tagged [performance]

Questions about the execution speed and memory usage of algorithms, data structures, languages and libraries.

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How does highly imbalanced test data in certain splits of k-fold time-series cross-validation affect model performance?

I am working on a time-series classification (TSC) problem using k-fold time-series cross-validation (TSCV) to evaluate the performance of my models. My training data for each split is fairly balanced,...
Tov Nephesh's user avatar
0 votes
1 answer
42 views

Standard deviation for online scenarios

Let's suppose you have to create an online algorithm $f(x_i)$ that will return the average ($\mu$); And the standard deviation ($\sigma$); Of numbers $x_0, \dots, x_i$. A straightforward approach ...
Matheus Diógenes Andrade's user avatar
0 votes
0 answers
67 views

How is kernel fusion done?

I have a computational graph (DAG) consisting of element-wise operations (potentially with broadcasting) and reshape/reduce operations (reshaping/sum/max). I'm trying to understand how vertical kernel ...
ilya's user avatar
  • 111
1 vote
1 answer
177 views

How do BLAS libraries implement support for transposed matrices?

I'm trying to understand how BLAS libraries implement fast GEMM with support for transposed matrices. Say, I'm only operating on square matrixes (with dimensions n ...
ilya's user avatar
  • 111
2 votes
0 answers
77 views

OpenMP Fortran array operations in target regions

I am asking this here for the possibility that someone here is familiar with OpenMP offloading. Is there some other way to parallelise Fortran array operations outside of unrolling the loops of the ...
Touko Puro's user avatar
1 vote
0 answers
92 views

Resource to learn assembly code

I'm a PhD student in mechanical engineering and I have to perform a lot of simulations for my project. In my lab we use several well-known libraries, from FEM to machine learning. As we're doing ...
FEGirl's user avatar
  • 405
5 votes
1 answer
305 views

Block-Tridiagonal Matrices with tridiagonal blocks

The Setup Using finite differences to discretize the 2d diffusion equation $$\partial_tu=\partial_x\left(A\partial_xu+B\partial_yu\right)+\partial_y\left(B\partial_xu+C\partial_yu\right)$$ we get a ...
Michael's user avatar
  • 153
12 votes
2 answers
1k views

Faster Logistic Function

I've noticed that a fairly significant number of cycles in one of my programs are being consumed by the logistic function: $$f(x)=\frac{1}{1+e^{-x}}$$ Is there a good approximation I can use to reduce ...
Richard's user avatar
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9 votes
2 answers
2k views

Is there an algorithm or graph theory that allows me to not need to store an intermediate matrix when calculating AT*Y1*A + BT*Y2*B?

I have a system of conductors for which there are two dense matrices of the (complex) mutual admittances, $Y_A$ and $Y_B$, which are symmetric. Then, an equivalent nodal admittance matrix $Y_N$ is ...
Pedro H. N. Vieira's user avatar
0 votes
1 answer
142 views

Efficiently solving SDP relaxation of an integer quadratic program

I have an integer quadratic program of the form, \begin{align} \underset{x}{\max}&\;\;\|Ax-b\|_2^2\\ \text{subject to}&\;\;x\in{\bf Z}\geq0 \end{align} I'm currently using the (admittedly ...
Set's user avatar
  • 503
3 votes
0 answers
189 views

How can I improve this matrix product calculation in OpenCL?

I am trying to compute a matrix-matrix product of N stacked complex double N x N matrices. For simplicity, I assume N = 512. I have written code in C++ parallelized with OMP and using OpenBLAS for the ...
sqrt6's user avatar
  • 31
1 vote
0 answers
85 views

Implementation of integration schemes for ordinary differential equations in Python and peformance comparison

I look for a book/manual where I can find implementations of different integration schemes for ordinary differential equations (like 4-th order Runge-Kutta) in Python with Numba. To be more specific, ...
Artem Alexandrov's user avatar
1 vote
0 answers
74 views

Calculating the number of Flops of SPH density calculation

I would like to calculate the number of floating point operations (Flops) my code is performing in my machine. To do so, I would like to be sure I am counting the operations in the inner-most loop ...
Hydro Guy's user avatar
  • 121
25 votes
8 answers
5k views

Is it possible for user written algorithms to outperform libraries' built-in optimized functions?

I've always had this question in mind (even if it may sound vague), but in my numerical analysis courses we've always learned how to analyze and optimize code. However, since most linear algebra ...
CynthiaZ1998's user avatar
-2 votes
1 answer
90 views

How to get 10 in computer science, using the number 4 exactly four times, and two signs exactly and two operation + exactly? [closed]

How to get 10 in computer science, using the number 4 exactly four times, and two signs exactly and two operation + exactly ?
Extrazlove's user avatar
0 votes
1 answer
232 views

What are the advantages and disadvantages of using norm error control in the MATLAB ODE suit?

In MATLAB's ODE suit, there seem to be two basic methods of controlling the Local Truncation Error (LTE) of the ODE which the user can choose from, namely: The absolute error control (default), ...
kostas1335's user avatar
2 votes
1 answer
45 views

In Eigen, can a sparse matrix contain vectors/objects instead of simple scalar values?

I need to have a sparse matrix whose elements are not simple numbers, but objects, e.g. a couple of floating point values and a bunch of integer indices. I am wondering if Eigen has something similar, ...
Pietro's user avatar
  • 171
13 votes
3 answers
36k views

How to properly calculate CPU and GPU FLOPS performance?

Problem I'm trying to calculate CPU / GPU FLOPS performance but I'm not sure if I'm doing it correctly. Let's say we have: A Kaby Lake CPU (clock: 2.8 GHz, cores: 4, threads: 8) A Pascal GPU (clock: ...
AlekseyHoffman's user avatar
1 vote
1 answer
99 views

An efficient algorithm to find Nearest Neighbours

So imagine I have a $m$ vectors each of dimension $d$. Lets call them, $\vec x_{i}$, with $i = 1, 2, 3, 4, 5, \dots, m$. Now the idea is to find the neighbours of $\vec x_{i}$ (calling them $\vec x_{j}...
sbp's user avatar
  • 263
5 votes
1 answer
145 views

Accurate and efficient computation of the logarithm of the ratio of two sines

For exploratory work related to special function implementations, I need to compute $\log \frac{\sin y}{\sin x} $, where $0 \le x \le y \le 2x < \frac{\pi}{2}$. Cases with $x \approx y$ in ...
njuffa's user avatar
  • 1,885
1 vote
1 answer
1k views

How to calculate the number of floating point operations a task/ process requires? (not FLOP/s, but FLOP)

There have been many papers quoting FLOP to quote the performance of a specific approach in machine learning. For example, We trained two models with different capacities: BlazePose Full (6.9 MFlop, ...
Ben Butterworth's user avatar
1 vote
0 answers
72 views

Why are "instructions retired" more stable than "cycles" or "task-clock" when using "perf"?

I tested the perf tool in Ubuntu 18.04 on a simple benchmark in our compiler (parsing some file). I ran perf several times and ...
Ondřej Čertík's user avatar
2 votes
0 answers
205 views

Whi are chi-squared distributions in (C++) boost::random and C++ STL faster than in boost::math?

I am trying to generate random chi-squared numbers in C++, according to some degree of freedom (which can be a float). Several libraries can be used for that purpose, among which the C++11 Standard ...
Clej's user avatar
  • 153
1 vote
0 answers
106 views

Fastest way to solve linear programming with 6 complex inequalities and 5 nonnegative variables

I have a program where I need to solve a linear programming problem in a fast loop. The language I'm using is Java and any kind of bindings to other languages are not acceptable. Libraries might be ...
juhist's user avatar
  • 151
2 votes
1 answer
398 views

Sparse matrix-matrix multiplication using AVX2

I have two sparse general matrices stored in CSR format I need to multiply. Is there any chance to gain performance using AVX2? In general the matrices are big (hundreds of millions of non-zeros and ...
vydesaster's user avatar
9 votes
1 answer
2k views

Increasing computational performance by using 16 bit numbers

I recently found the following article where it was stated that using 16 bit numbers can be used to increase the computational performance of AI applications. According to the article numbers above 16 ...
vydesaster's user avatar
0 votes
0 answers
692 views

Parallel plate capacitor as simple superposition of Coulomb-fields

I am trying to calculate and visualize the electric field inside and outside of a parallel plate capacitor by assuming a uniform distribution of point charges on each plate and by adding up the ...
dp21's user avatar
  • 11
4 votes
2 answers
692 views

Fastest Way to Mutiply $10^4$ 2x2 Matrices

In a code that I work with (written in python, but also tagging as matlab because numpy is so close and I could use it if need be), we use a transfer matrix method to compute the properties of a ...
ElectronsAndStuff's user avatar
2 votes
0 answers
72 views

Avoid matrix multiplication in algebraic multigrid method

Currently when I try to solve a linear algebra system of the form of $A x =b$ I use the algebraic multigrid method. The algebraic multigrid method uses a Galerkin product to form the coarse grid ...
vydesaster's user avatar
4 votes
1 answer
98 views

Is operation count a reliable predictor of performance when comparing two formulations?

I have two formulations to solve a problem (both give dense, complex and symmetric system). They are solved multiple times in a loop. I am trying to predict which is better to use. The first one ...
Pedro H. N. Vieira's user avatar
1 vote
0 answers
23 views

Speedup of CPU Pipelining by number of steps [closed]

When a CPU has $K$ steps the speed up of using pipelining compared to non-pipelining is $K$. But what I want to know is, say I am a CPU designer and want to decide whether I should build $K$ or $N$ ...
Michael Ebenstein's user avatar
1 vote
1 answer
206 views

Vectorization of Jacobi iteration

Assume I have a linear system of $A x = b$ which I want to solve with Jacobi iteration. Matrix $A$ is given in CSR format. The vectors are dense. The code for Jacobi iteration is quite clear and can ...
vydesaster's user avatar
2 votes
1 answer
144 views

Efficiently finding binary vectors satisfying multiple conditions

I am trying to solve the following problem: Given a binary matrix $\mathbf{A} \in \{0,1\}^{m \times n}$ and a vector $\mathbf{b} \in \mathbb N^n$, does there exist a binary vector $\mathbf{c} \in \{0,...
afallafa's user avatar
1 vote
1 answer
76 views

How to avoid unnecessary checks when inverting this LU decomposition

Background for the question I am currently working on a Matlab code in which the systems of linear equations $Ax_1 = b_1$, $Ax_2 = b_2$, ... have to be solved. As the matrix $A$ is constant during ...
Mathias Klahn's user avatar
2 votes
1 answer
578 views

Implementation of Jacobi iteration

I have implemented the Jacobi iteration in C++ using a dense vector and a sparse matrix in CSR format. The code is as follows: ...
vydesaster's user avatar
4 votes
1 answer
487 views

Improve Mandelung constant code

I'm learning and improving my Python skills. I did a program in Python about Mandelung constant. But, I'm having kind of a problem. The Mangelung constant is calculated using this sum: $$ V_{total} =...
Daniel M M's user avatar
7 votes
0 answers
595 views

Is there any catch on using `zgemm3m` vs regular `zgemm`?

I've just (to my embarrassment) encountered a BLAS-like extension of a matrix-matrix product subroutine gemm in Intel MKL: gemm3m...
Anton Menshov's user avatar
  • 8,672
1 vote
1 answer
181 views

How to implement this even-odd matrix decomposition efficiently?

Note: This question has also been asked on stackoverflow - see https://stackoverflow.com/questions/57197910/how-to-implement-this-even-odd-matrix-decomposition-efficiently?noredirect=1#...
Mathias Klahn's user avatar
2 votes
2 answers
128 views

Time complexity analysis

I want to know the time complexity of following code Say I have a list unique_element[] There is an array which contain elements {4,5,2,4,7,8,1,5,9,8,1} Now as per my code I want to find out the ...
Encipher's user avatar
  • 123
6 votes
1 answer
291 views

Whittaker-Shannon interpolation: Accuracy dies with speedup; can it be fixed?

With a truncated Whitaker-Shannon series (cardinal series) $$ f(t) = \sum_{j = 0}^{n-1} y_{j} \frac{\sin\left(\pi( \frac{t-t_0}{h} -j)\right)}{\pi\left(\frac{t-t_0}{h}-j\right)} $$ we can naively ...
user14717's user avatar
  • 2,155
3 votes
1 answer
468 views

Radiation heat transfer between surfaces

I'm trying to model the temperature distribution over a curved surface. Apart from the heat equation, I need to take into account the energy emission/absorption through electromagnetic radiation. The ...
JuanGM's user avatar
  • 31
6 votes
2 answers
2k views

Fast and Numerically Stable Pairwise Distance Algorithms

I'm looking for resources on fast, numerically stable pairwise euclidean distance algorithms. In particular, suppose $A \in \mathbb{R}^{M \times D}$ and $B \in \mathbb{R}^{N \times D}$ are two sets of ...
Chris Swierczewski's user avatar
10 votes
2 answers
9k views

Integer operations vs floating point operations

I have been working with an algorithm, which uses additions of floating point vectors, (sparse matrix of floats)x(dense vector of floats) dot products I recently found out that I can get the same ...
Dionysios Georgiadis's user avatar
3 votes
1 answer
695 views

MKL/FFTW performance of batch 1-D FFTs

MKL and FFTW offer 1-D FFTs that can operate on many inputs simultaneously - in other words, they can batch-transform the columns of some input matrix. Is the performance of these multi-transforms ...
smh's user avatar
  • 673
3 votes
1 answer
747 views

What is the fastest way to solve Ax=b (subject to constraints and an absolute term)

I am trying to solve/optimize $Ax=b$ in the least squares sense subject to box constraints; a few (less than 5) equality/inequality constraints; and an absolute function penalty (or some other ...
Big AL's user avatar
  • 133
0 votes
1 answer
313 views

CPU and GPU influence on task parallel execution performance

This question is mainly about hardware, but also about software. In my current work I have approximately 68 millions of combinations that I am iterating through, in parallel. For each of those ...
Alex's user avatar
  • 101
1 vote
1 answer
2k views

General understanding of Intel MKL, threads and MPI

Preface I seem to lack a fundamental understanding of best practise recommendations given by Intels MKL user guides for using MKL in threaded applications. So let's clarify it together. Wording and ...
pbx's user avatar
  • 113
2 votes
1 answer
514 views

Potential gain - Matlab vs C/C++ - assembly and eigenvalues

I have a Matlab code computing the solution to an eigenvalue PDE. It consists of two parts: assembly of the stiffness/rigidity matrices and solving a generalized eigenvalue problem. I mention that the ...
Beni Bogosel's user avatar
  • 1,067
1 vote
1 answer
2k views

Kronecker product among multiple arrays

I was wondering whether there is a smart and efficient way in Matlab to compute the kronecker product of several 1D arrays. What I mean is something like this ...
FancyPants's user avatar
1 vote
2 answers
207 views

Sign of integer determinant 4 by 4

I'm in the context of this publication: http://www.gilbertbernstein.com/resources/booleans2009.pdf I applied quantization to my point coordinates: All coordinates are integer lying in [0, 2 power 20]....
Brainless's user avatar
  • 111