# Questions tagged [performance]

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

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### 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 ...
61 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 ...
76 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 ...
1 vote
59 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, ...
1 vote
36 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 ...
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 ...
76 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 ?
137 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), ...
38 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, ...
14k 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: ...
1 vote
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1 vote
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### 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 ...