Questions about optimizing code for faster results, or how to do faster computations.

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0
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0answers
55 views

Low CPU usage. How to increase it? Should I?

I'm running a programme, and below are some graphics from the resources monitor from windows 8, while running my programme in version 9 of mathematica. Sorry for the foreign writings in the pics, but ...
0
votes
1answer
39 views

How to speed up ReplaceAll in Table?

I am writing a code which solve a list of equations and then create a Table with resulst of equation solving. In applications where I use this code, I create a bunch of equations and my computations ...
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0answers
20 views

Tricks to speeding up optimisation of a function involving a heavy integration

This is the code, and energycoeffs[] is the function that takes in a dxd matrix and spits out a scalar value. ...
3
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2answers
53 views

How do I apply a ColorDataFunction[] to a grayscale image? [duplicate]

Suppose I have a 2D array im of real values between 0 and 1, representing a grayscale image. I can turn im into an image very ...
2
votes
1answer
75 views

Optimizing alphametrics code

First of all, thank you all in this great community. I have been reading a lot of threads about Mathematica optimization learning things like using Compile ...
0
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0answers
31 views

Retrieving a Portion of Webpage Code using URLFetch

The URLFetch command is very useful for pulling the entire html source of a given webpage, however, if one wanted to speed up the process, by only requesting a ...
20
votes
3answers
740 views

DeleteDuplicatesBy is not performing as I'd hoped. Am I missing something?

Déjà vu: a new-in-v10 function should provide a better solution to an old problem, but my enthusiasm is curbed when I run timings. This time the function is ...
2
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1answer
46 views

What is the fastest way to get notebook CellGroups / Cells structure?

So the question is how to get this kind of information: from This is one of my ideas: ...
9
votes
1answer
107 views

Slow work of SQLInsert with MS SQL Server in V10

This question is very similar to: Slow work of SQLInsert with SQLite, but for MS SQL Server. Unfortunately the use of SQLBeginTransaction and ...
9
votes
3answers
281 views

Slow work of SQLInsert with SQLite

I want to store my data in SQLite database, but writing large numbers of data its too slow. For example: ...
7
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0answers
89 views

How to make Graphics3D with multiple lighting sources being rendered faster

I have a very "precise"(through setting "SpherePoints") Sphere illuminated by hundreds of random color lighting sources. The ...
1
vote
1answer
49 views

How to handle Indeterminate TimeConstrain

I have to use Timeconstrained[aux] first for avoid some bigs calculation that dont need and it use a lot of time of calculate, so i can't do this. ...
1
vote
1answer
52 views

Is this caused by meomory usage ? (Something odd/hard to describe)

I really can't make a "smaller" example, but the files are here, for the data and for the notebook. It will cost a LOT of memory, up to 30G of RAM (maybe more). Here is the problem, (from a Linux ...
4
votes
1answer
206 views

Mathematica 10 issue: working with Entities slows down recurrence equations [duplicate]

I was looking at the Mathematica code given at http://community.wolfram.com/groups/-/m/t/326240 where example code is given to simulate the spreading of a supposed Ebola outbreak in Nigeria: ...
0
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0answers
88 views

CPU usage ~18%, but Mathematica is fully running

I run some very long Mathematica code, and the CPU usage of the kernel is 18% only. Why is not all of the CPU used, can I find the reason easily? Are there known ways to tell Mathematica to use more ...
7
votes
1answer
189 views

Is there a faster way to Map an Association?

Consider mapping an existing Association in a manner such as this: ...
4
votes
5answers
284 views

Check whether array has only constant entries?

I have an array arr with n entries. Now I want to check whether ...
2
votes
1answer
112 views

How to speed up my code about Divisors?

This code is about PE496 In[21]:= ParallelSum[n*Count[Divisors[n^2], a_ /; n < a < 2 n], {n, 1, 10^5}] // AbsoluteTiming Out[21]= {5.987342,10724527832} I ...
8
votes
0answers
192 views

Choose between `Apply` and `Map`

Even though this might be too general question(or not answerable), I want to get some advice here. I apologize in advance if it is not a relevant question. I frequently have to process large list of ...
1
vote
3answers
82 views

Speed up NIntegrate, which takes eigenvalues from another function

I have simplified my problem here, in my actual problem the matrix is much bigger which makes it impossible to find eigenvalues analytically. So, I chose standard BCS problem (2x2 matrix) to ...
17
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1answer
267 views

Why some built-in functions are slow

I just wonder why some built-in functions are slower compared to some other ways using more than one built-in functions for doing same job. consider this example: ...
0
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1answer
88 views

How to speed up execution of this function?

How can I speed up the execution of following function, specifically for larger values of n? ...
20
votes
1answer
399 views

Total much slower in version 10

Compilation nowadays may give very fast functions. Here is an example for finding the sum of a list of machine numbers, just as the built-in function Total: ...
4
votes
1answer
90 views

Why is C-compiled (but not WVM-compiled) code so slow in Manipulate?

Here is a small section of code from this SE question which computes the real part of the dilogarithm (the upper limit of the sum is increased for demonstration purposes): ...
4
votes
1answer
110 views

How do I understand this big difference in speed:

A friend of mine found a huge difference in runtime speed between these two ...
3
votes
2answers
169 views

Help at speeding up simplification/nested symbolic integration

I have the following problem: I want to compute an integral of the form $$\int\limits_0^{t_g}\mathrm{d}t_2\int\limits_0^{t_2}\mathrm{d}t_1\left[A(t_1),A(t_2)\right],$$where $\left[B,C\right]=BC-CB$ is ...
25
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3answers
3k views

Understanding differences between Maple and Mathematica in examples picked by Maplesoft

I am reading the document "How Maple Compares to Mathematica" found at http://www.maplesoft.com/products/maple/compare/HowMapleComparestoMathematica.pdf. On page 15 there is an example where ...
0
votes
1answer
62 views

Duplicate values n-times [closed]

I already asked how I can take the list {1,2,3} and get {1,1,1,2,2,2,3,3,3} out of it, adding degeneracy to the problem. So far ...
7
votes
4answers
526 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 ...
0
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0answers
47 views

More on performance of Sum[]

There is an interesting discussion on performance of Sum[] in this question. I actually wanted to reproduce findings from this answer. So, I entered: ...
1
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1answer
50 views

Speed optimization of Mean calculation in a previous calculated data range

I have following problem: My calculations work quite well with the shown testdata, the only problem is the speed of it. My original dataset is about 64000 datapoints, and it takes several minutes to ...
5
votes
3answers
247 views

The speed of Sum[] varies strangely

I was curious about the difference in speed between Total and Sum. I found out Total was ...
5
votes
1answer
469 views

Over 30mins to generate the first eigenvector?

Is it normal for Mathematica to take over 30mins to try to compute the first eigenvector of a 100x100 matrix? The matrix is reasonably sparse - about 90% of the cells are 0s and each column sums to ...
0
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0answers
60 views

Improve on timing of NMinimize

I got a little performance problem with the function NMinimize (it takes mathematica approximately 10 minutes to compute the results). Here i s my sample code: ...
2
votes
1answer
134 views

Neighbourhood - Calculations

SeedRandom[0]; n = 5; (m = N @ RandomInteger[{1, 3}, {n, n}]) // MatrixForm result1 = MeanFilter[m, 1] // MatrixForm ...
0
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0answers
53 views

Speed up numerical optimization (for plotting and solving)?

Briefly speaking, I want to plot a function PIfun[], which its value is based on numerical optimization using NMaximize. It ...
9
votes
4answers
288 views

How can I efficiently check if a graph is unit distance?

A unit distance graph is a graph that is embeddable in the plane so that every edge has length 1. ...
4
votes
2answers
411 views

Colorize Grayscale Image

I have a grayscale image that contains two objects. The grayscale pixel values can be divided into three intervals where two of them represent objects and the third represents the background. The ...
11
votes
3answers
2k views

Speed up ordering digit code?

My goal is given an integer number to deduce if its digits increase (or remain the same) from left to right or not. Example: $1236, 123336$ are both considered numbers with increasing digits, but ...
2
votes
1answer
136 views

2D Fourier transform of a few (4) disjoint discs on a plane

I'd really appreciate some advice. Short Version I'm trying to calculate the following $$ ...
6
votes
1answer
223 views

Collision detection algorithm (discrete) with sweep and prune algorithm

For a more complex collision detection approach, I need an efficient (aka fast) algorithm to prune the elements by using boundary boxes. A classical algorithm is the so called sweep and prune (SAP) ...
3
votes
3answers
298 views

Faster Integer Approximation of pi

I'd like to speed up this calculation: First[Sort[Table[{k,Abs[Round[k/Pi]Pi - k]1.{k,1,100000}],#1[[2]]<#2[[2]] &]] The code above generates a list of ...
1
vote
1answer
99 views

NSolve for complicated equation involving double cross product

I have the following issue. I am trying to solve a 3-vector equation for the vector slx, sly, and ...
34
votes
2answers
847 views

Why is the new PositionIndex horribly slow?

This issue has largely been mitigated in 10.0.1. New timings for the final test below are: ...
6
votes
3answers
214 views

Speed of ConvexHullMesh

Pick $N$ random points on the surface of the sphere, then use ConvexHullMesh[] to compute their convex hull. Empirically, this takes time quadratic time in $N,$ ...
9
votes
4answers
294 views

Replacing matrix values

I want to find the n largest values in a matrix and replace all others with zero. The solution I found uses ReplaceAll and becomes very slow as the size of ...
17
votes
5answers
1k views

How to speed up my Project Euler code

The evaluation speed of Mathematica often depresses me. It did it again when I wrote a code to solve a Project Euler problem. https://projecteuler.net/problem=206 Here's my code: ...
9
votes
2answers
194 views

Extracting values with multiple keys

I want to extract sorted data from a huge database based upon two (or more) keys in a very timely manner. Here is a reproducible toy example for two keys only: ...
15
votes
1answer
364 views

Speed up adding Poisson noise to an image

I'm simulating some images corrupted with Poisson noise, but I'm encountering a few problems with performance. According to the documentation on ImageEffect, one ...
5
votes
0answers
217 views

Problems extending NelderMeadMinimize into 2D

Update The eventual route I followed was to adapt a version of the NM-simplex written in C and link to it with MathLink. Once I've tested this out fully I'll post it here. I've been playing around ...