Questions on optimizing Mathematica code for higher performance. This may mean faster execution, lower memory usage or both. Not to be confused with mathematical optimization.

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2
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0answers
71 views

Why does setting $Assumptions make my Fourier transforms slow?

Consider these Fourier transforms ...
1
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1answer
79 views

Efficient calculation of diagonal matrix elements

I have a matrix $V$ of size $M$ in which each row $i$ is a vector $v_i$. Now I have another matrix $H$ and I would like to calculate as efficiently as possible the list of values $v_i^\dagger\cdot ...
0
votes
0answers
77 views

Optimization of vector manipulation

I'm trying to implement an upwind scheme for solving transport equation (at first, I work with no right hand side and the simpliest case possible - velocity is constant, initial data is smooth, etc). ...
5
votes
0answers
153 views

Challenge: Speeding up MaxDetect for application in 3D blob detection

In image segmentation it is a common problem that objects appear clustered and are therefore undistinguishable from each other when using simple algorithms. Based on this post I obtained efficient ...
5
votes
1answer
163 views

How to speed up this TDSE code?

I'm trying to build a 1D time-dependent Schrodinger equation solver, using the Crank-Nicholson method. And I think the code is kind of working now, but the speed is still slow for me. Here is the ...
2
votes
1answer
131 views

Performance on Binomial Deviate is slow

I hope I won't get spanked for reposting. This is related to a previous question discussed here: Performance on Multinomial Deviate is slow. but this version is simpler because it is a binomial ...
6
votes
0answers
204 views

Speed up MinimalPolynomial

My Mathematica code runs slowly MinimalPolynomial[Sqrt[2] + Sqrt[3]+ Sqrt[5]+ Sqrt[7]+ Sqrt[11]+ Sqrt[13], x] runs slowly, but the Maple version ...
3
votes
0answers
82 views

LibraryLink parallel performance

I'm trying to use a LibraryLink function in parallel. It is an embarrassingly parallel problem, so that no dependency between those parallel tasks. However I can only get the parallel efficiency about ...
4
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0answers
114 views

“Off-label use” of Mathematica functions for performance

Assisting an acquaintance with a simulation where a very large number of binomial probability calculations are required, I pointed them to a slightly obscure function to dramatically speed up their ...
4
votes
2answers
131 views

Values (or positions) of array row elements within a specified number of positions from target value

I have the need to collect values from the rows of rectangular arrays of arbitrary precision integers, given a target element value and allowed "distance" (positions +/- within the row from found ...
4
votes
2answers
269 views

DynamicModule/Dynamic CheckboxBar Slow for Large Lists

I am trying to create a dynamic construct that takes a large list of expressions and allows the user to interactively select any number of entries for further manipulation. This is what I have ...
2
votes
0answers
361 views

Speeding up Nonlinearmodelfit by constraining parameters?

I have a complicated parametric PDE that can be fitted to some data with NonlinearModelFit, but takes several hours to estimate the best values of the four free parameters. Currently, the code ...
11
votes
5answers
2k views

What is the fastest way to extract a substring from a huge string?

I develop an algorithm to find the most common substrings of a given length n up to a certain distance l in front of a pattern p in a huge sequence S. E.g. I want to find the most common hexamers ...
6
votes
3answers
247 views

Enumerate the 1-factors (perfect matchings) of $K_n$

Introduction I would like to enumerate the 1-factors, or (near-)perfect matchings, of the complete graph Kn. The adjacency list representation for Kn is basically { (x, y) | 1 ≤ x < y ≤ n }. For ...
2
votes
2answers
128 views

Counting Events in a moving date range

I want to count the number of times events take place in a date range. The counting is done over a window of e.g. 28 days where the goal is to have between 11 and 13 events in the time window. The ...
1
vote
2answers
82 views

Extract the real components from a very large expression

Suppose I have a very long expression (>500,000 characters) which contains a mixture of real and imaginary terms. e.g ...
0
votes
0answers
70 views

Is there a faster way to do Normal[SparseArray[{{1,1,1}→1.2, {1,1,2}→20.2, …, {m,n,p}→0.3}]]?

I have a list of the form {{1,1,1}→1.2, {1,1,2}→20.2, ..., {m,n,p}→0.3} and I want to create an $m \times n \times p$ array, $A$, where the value of $A[[i,j,k]]$ is ...
9
votes
5answers
749 views

Fast way of finding position of Interval containing an Integer

I have a large list (about 2.2 million) of pairs of integers. Each pair defines an Interval[{}]. Given some integer x, I need to ...
1
vote
0answers
59 views

Approximate to the speed of Build-In functions

In Mathematica, there is a function PowerMod[a,b,m], which computes a^b mod m. I will concern only this case: ...
1
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1answer
134 views

Code Performance Tuning

The following code takes over 4 seconds to run. Any one has suggestions to make the expressions for qf, phi, ...
10
votes
1answer
287 views

Drop selection of columns from a ragged array

I have an application where I need to drop some arbitrary list of columns from a ragged array (where of course the shortest array rows have at least all the specified columns). E.g., given a ragged ...
0
votes
0answers
46 views

Addition of sparse array objects [duplicate]

I have been having some trouble with the addition of large (but very sparse) matrices using SparseArray. Here is the simplest example to illustrate the issue. First, I will define diagonal matrices ...
5
votes
2answers
171 views

Improving performance in the generation of random (directed acyclic) graphs

I need to generate large (directed, acyclic, transitive) graphs. My code in Mathematica gets very slow for large numbers of vertices. I've tried a number of approaches and I can't find any significant ...
1
vote
1answer
146 views

Simulation code performance tuning

The following simulation takes over 20 seconds for evaluation. I have difficulty re-coding it with Nest and Map or Compile functions to make it more efficient. Can some one help with this? The ...
10
votes
8answers
385 views

Fast way to get positions of “boxed” array elements?

Given a 2D array (arbitrary numeric / evaluates to numeric elements, simplified for examples, and can be arbitrary dimensions so long as the operation makes sense, I'm working with 2K X 2K in my ...
7
votes
4answers
567 views

Suppress connection to Wolfram|Alpha when making unit conversions

I want to speed up calculations with unit conversions. I suspect primarily that some units evaluate from Wolfram|Alpha. Any way to prevent this automatically, so that Mathematica throws ...
22
votes
1answer
480 views

How to work with Experimental`NumericalFunction?

This question is intimately connected with previous one: "How to create internally optimized expression for computing with high WorkingPrecision?" Oleksandr R. correctly states in the comment: A ...
4
votes
3answers
524 views

Why is my solution to PE #5 so slow

I'm new to Mathematica and it was suggested to me to go through the Project Euler problems in order to learn it. However, I can't quite figure out why my solution to #5 is so slow. The problem: ...
2
votes
3answers
337 views

Re-arranging / selecting of a data table very slow in For loop [duplicate]

My task is quite simple; I have a table of data like M = {{1,2}, {1,3}, {3,4}, {5,1}, {6,9}, {6,8}, {6,1}}; so the table is sorted with respect to the first ...
5
votes
1answer
108 views

Why does a heavy background slow LocatorPane from updating, even if only the locators are Dynamic?

I'm having some trouble getting a dynamic plot to operate efficiently, and I think I've tracked down at least part of the problem to some pretty weird behaviour on the part of ...
8
votes
5answers
2k views

Something faster than Do loops with AppendTo

I am an "old" programmer used to Fortran and Pascal. I can't get rid of For, Do and While ...
0
votes
0answers
44 views

Using Table[ ] vs using Do[Append [ ] ] [duplicate]

Is it generally better/faster to use the Table function over using Do[Append []]? For example, I have this piece of code: ...
0
votes
1answer
110 views

Why does initialization slow down manipulate in this case?

I'm trying to manipulate a plot of function with some parameters. The function is a long expression, so I tried to put it inside the Initialization options of ...
7
votes
5answers
325 views

LengthWhile until first duplication

I have the need to trim each of a large number of potentially very long lists (10^6+ elements) to the length where the last occurrence of any distinct element happens, or said another way, where the ...
7
votes
1answer
233 views

Better way to get Fisher Exact?

I want to perform a Pearson's $\chi^2$ test to analyse contingency tables; but because I have small numbers, it is recommended to perform instead what is called a Fisher's Exact Test. This requires ...
2
votes
2answers
125 views

Random Choice: List Format & Minimizing Memory Use

This is a two part question, and for that I apologize.. but they're related! Here's what I'm working with: ...
8
votes
3answers
306 views

Pairwise distances of points and classification using GraphDistanceMatrix

The challenge Given $n$ points in $\mathbf{R}^3$ and a cutoff distance, $d$, I would like to determine all pairs of points that are separated by less than the given cutoff distance, $d$, and all ...
4
votes
1answer
277 views

How to choose MaxStepFraction for optimal speed of NDSolve

I'm trying to use NDSolve to solve a 1D Schrodinger's equation, and it seems that MaxStepFraction has huge effect on the ...
4
votes
2answers
227 views

About auto-compiling and performance between Do and Fold

I was investigating how Fold could improve performance vs Do. I tested the code ...
6
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0answers
429 views

Poor CUDALink performance, when calling a kernel multiple times

When working on a project of mine I noticed that CUDALink shows very poor performance when calling CUDA kernels multiple times in a loop-construct. To demonstrate this I put together this little ...
78
votes
1answer
1k views

Why are numeric division and subtraction not handled better in Mathematica?

There is something that has been troubling me for a while. At least through version 10.0 the performance of a / b and a - b is ...
6
votes
1answer
120 views

Finer granularity with ParallelDo

ParallelDo only parallelizes by the innermost variable. Is it possible to distribute the calculation over all the points (all the variable) separately? let me ...
8
votes
6answers
250 views

Faster list duplicate 'limiter'

Given some list, e.g., {5, 3, 2, 3, 1, 0, 1, 3, 5, 5, 4, 5, 1, 2, 5, 2, 2, 0, 1, 4}, I need to limit the duplicates, if any, to an arbitrarily chosen number. The ...
7
votes
1answer
198 views

Law of Cosines to determine angle change along spiral

The Spiral I'm trying to place circles along the outside of an Archimedean spiral. Shown below: ...
21
votes
5answers
705 views

More efficient way of generating list of occurrence counts?

Given a list, e.g., target = {a, b, c, b, c, d, c, d, e, f, a, h, g}, I want to generate a list containing the occurrence count of the corresponding element of the ...
4
votes
4answers
317 views

Using Locators in a non-standard Manipulate code

I'm trying to adapt Nasser's method for using a control variable inside Manipulate to selectively choose what part of the code should be recalculated depending on the controls changed (see this ...
1
vote
1answer
197 views

Using Manipulate with a control variable for selective recalculation

I'm trying to adapt Nasser's method for using a control variable inside Manipulate to selectively choose what part of the code should be recalculated depending on the controls changed. I've also read ...
9
votes
2answers
282 views

How to avoid an expensive subset of a Manipulate computation when dependent variables have not changed?

I have a Manipulate where a portion of the calculation that ends up displayed is dependent on a subset of the Manipulate control ...
18
votes
1answer
542 views

Fast DensityPlot

Is it possible to increase the perforamce the DensityPlot? For example, let's try to plot this "flower" ...
38
votes
2answers
2k views

Benchmarking Mathematica performance on the Raspberry Pi

It is not surprising that Mathematica on the Raspberry Pi is slow and clunky. In Stephen Wolfram's words, the command line is "quite zippy" but the notebook interface is "a trifle sluggish by modern ...