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Writing Fast MATLAB Code

11 Aug 2004 (Updated 07 Jan 2008)

Speed up your project with this collection of techniques.

File Information

Description

Learn how to use the Profiler tool, vectorized functions, and other tricks to writing efficient MATLAB code. This article includes how to convert any array into a column vector, bounding a value without if statements, and repeating/tiling a vector without repmat.

Contents:
* The Profiler
* Array Preallocation
* JIT Acceleration
* Vectorization
* Inlining Simple Functions
* Referencing Operations
* Numerical Integration
* Signal Processing
* Miscellaneous Tricks

MATLAB release

MATLAB 7.5 (R2007b)

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Comments and Ratings (68)
13 Aug 2004	Please Remove	You should look into NUMEL rather then prod(size(x)). Also be careful about recommending any or all or even min and max. they operate on vectors and NOT the entire matrix! You suggestions about not repmat are awful. I tried each one of your examples and found that was the same speed or faster. My matrices had around 5 million numbers in them. The last thing I would recommend is the use of MEX files. While it can be faster, it will take that much longer to write, peer, and debug. Did you check the speed of looping in matlab?
14 Aug 2004	Pascal Getreuer	*Response to review* I'm sorry this article wasn't helpful, perhaps it is too introductory for you. Responding to your points: (1) ?numel? is not a function as of MATLAB 5.3 (what usually work with). It is a standard function by version 6.1. (2) It is true that min and max operate over columns rather than entire matrices (the article includes some discussion on this). Thus the suggested methods involving min and max include matrix to vector conversion (using "A(:)" changes A to a vector). It works for matrices and n-D matrices of all sizes. (3) The advantage of the not repmat method is that there is no function call -- it won't be significantly faster for a single tiling but can make a difference for many separate tiling operations. Furthermore, the standard m-files in MATLAB 4.0 and earlier don't include repmat, so this method is also more compatible. (4) MEX is not a topic of discussion in this article, only mentioned. I agree it is much more difficult to write and peer and should only be a last resort. (5) And yes, looping has a fair bit of overhead. Try the profiler on a for loop with many iterations and a one-line inner loop.
16 Aug 2004	Saeed Attarzadeh	It's great
19 Aug 2004	James Alaly	Thanks, this is a great basic guide to speeding up Matlab code. I wish I had it a year ago when I started with Matlab. As a note though, the method shown to avoid repmat is rarely faster (in Matlab 6.5) and usually slower than actually using repmat. But thanks for the work you put into this, I printed it out and keep it next to Richard Johnson's "Matlab Programming Style Guidelines" on my ML shelf.
05 Jan 2005	Rene Just Nielsen	A nice (and brief) collection of useful tips.
24 Jan 2005	Troels Pedersen	Very good description of the indexing features of matlab. Please not that transposing a matrix using ' will complex conjungate the elements aswell. Therefore to create a row-vector by A(:)' should be done with care. Alternatively I think that transpose(A(:)) should be used.
02 Apr 2005	Nabil nabil	very good document
06 May 2005	O. L.	As a beginner, I have found everything clear, fast reading, and useful. Good job!
10 May 2005	karthik lakshmanan
04 Jul 2005	ALoser IAm	Helpful.
11 Jul 2005	Izru Garner	Useful
12 Sep 2005	maomun munmao	fillfull
19 Sep 2005	smita parija	itis moreuseful
07 Oct 2005	Ahmed Ayoub
08 Oct 2005	sivasankaran sivanandam
14 Oct 2005	Nemo Managna	Yes it's a good idea to use the profiler. Using the profiler, I found that Pascal's recommended matrix initial code A = s(ones(m,n)) is four times slower than the simpler A(1:m,1:n) = s or A = s +zeros(m,n)
10 Nov 2005	Gerald Corzo
30 Nov 2005	Jas Ellis	A very good outline of advanced Matlab tips. Well worth reading.
13 Dec 2005	Syed Husain	It's a great helping tool.
05 Feb 2006	Jq Yin
07 Feb 2006	deepak panwar
26 Feb 2006	Ramin Moshfegh	Great Job
05 Apr 2006	asd asdf
11 Oct 2006	Guillermo Ruiz	Thanks you are really good people
12 Oct 2006	Orlando Rodríguez	Excellent stuff.
09 Nov 2006	Alonso Morgado	Very good
15 Nov 2006	Sarah Miles	Excellent work. You may want to correct the submission date. Thought it was old but realised when opened it that it was writen in June 2006.
14 Dec 2006	ali ahsan	fair try
21 Dec 2006	A M
03 Jan 2007	Vishnuvenkatesh Dhage
23 Jan 2007	Simone Rabaovic
01 Mar 2007	Christoph Ullrich	Very good short introduction to optimizing m-files!
02 Mar 2007	Azalin L	there were some grammar errors...but I guess your a French speaker apart from that...it was descent
06 Mar 2007	Robson Mariano
12 May 2007	emanuel luduvicce
03 Jul 2007	Sam Clanton	I love it, Azalin.. way to face off against bad grammar with even worse...
20 Jul 2007	Norbert P.
03 Aug 2007	Kyoung ho Chong	Very useful tip!! I love it
06 Sep 2007	yiseth brango	excelente
19 Sep 2007	yugandhar yadam
22 Sep 2007	dawuni mohammed	i'm a student interested in this field.
24 Sep 2007	oktay gültekin	very usefull thx
01 Dec 2007	Hari Kumar	Well written article. Quite useful. Thanks.
01 Jan 2008	burhan rasito	wow its very exciting
15 Feb 2008	ntobeko zulu	none
23 Mar 2008	Dan Cohn	Kudos, very informative and well written. Thank you for your good efforts!
26 Mar 2008	biswa bhusan	nice
01 May 2008	chandra Guntupalli
01 May 2008	chandra Guntupalli
08 May 2008	Elias Pipping
19 Jun 2008	khaled darwish
06 Jul 2008	marie billa	good
15 Jul 2008	Issac Niwas S
16 Jul 2008	taneat zaetung
26 Jul 2008	abiodun olaluwe	kudos guy. I believe this meet sure meet the yearning fast majority of novice MATLAB users the world over.
07 Aug 2008	ritesh shah
07 Aug 2008	nick .	Nice little read with some random tips.
14 Aug 2008	Abel Brown	Indeed, a very good read ... should talk about things like bsxfun and how mex files compare to past and current matlab speeds. How about a section on I/O and string parsing.
02 Sep 2008	Husam Aldahiyat	This is so amazing and helpful. I've been struggling with slow executing functions and million element matrices for a long time but now it's all solved. Thanks a lot Mr. and know that you've been a lot of help. A LOT.
08 Sep 2008	AMIT RAJ
28 Sep 2008	Gamal Alkirshi	Thank you about this informations
04 Oct 2008	Khanh Vo	Thanks a lot for this. A much for any people speaks MATLAB.
04 Oct 2008	Khanh Vo	I forgot rating. :)))
11 Oct 2008	Juan Pablo Arias
25 Nov 2008	Sunil	thank u for such kind information. really helpful tips and please would you suggest me that i have a problem regarding execution time of for loop which i have to execute for 262144 times and its taking too much time about 2 mins so what should i do to reduce the execution time even i have used the preallocation of resultant matrix.
28 Nov 2008	Luigi Giaccari	Thanks sometimes pdf are better than m-file.
29 Nov 2008	alyaa
31 Dec 2008	Nguyen Thang	Good, Thanks!

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Updates
07 Sep 2005	Various fixes and revision
01 Dec 2005	Inlining Simple Functions section added
24 Jan 2006	Various revisions, integration section added
09 Jun 2006	Signal Processing section added
07 Jan 2008	Updates for MATLAB 7, including a new section on JIT

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