Doug's MATLAB Video Tutorials

October 19th, 2006

By Doug Hull

Doug first used MATLAB in 1994, could not figure it out until he got some help in 1995. He is now dedicated to making sure that no one else wastes a year of their life not knowing MATLAB like he did.

15:46 UTC | Posted in Format: Video | Permalink | 31 Comments »

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31 Responses to “Profiler to find code bottlenecks”

1. Siamak replied on October 19th, 2006 at 16:21 UTC :
   

   I like these simple videos; they actually show me how a pro uses the same tools that I use everyday, it develops my skills

   I have used profiler before but I really think that using profiler efficiently needs some skills or at least you have to have some sense of code optization, otherwise you will be trapped in a bottle-neck like correct code

   A good suggestion for these video series would be how to use a source control system in MATLAB, I am anxious to watch something on it

2. Mark Ray replied on October 19th, 2006 at 17:44 UTC :
   

   Great idea for a first video to share!

   How about sharing a little info about how you made the video?

   Thanks

   Mark

3. Doug replied on October 20th, 2006 at 12:19 UTC :
   

   Mark,

   I used Camtasia for the recording.

   Doug

4. Andreas replied on October 20th, 2006 at 18:24 UTC :
   

   Hi Doug,
   I am using the profiler a lot, it’s very helpful. But sometimes it returns strange results. Occasionally it tells me that most time (such as >60%) is spent at an “END” statement. I have not yet been able to find information anywhere that explains why the code would spend so much time at a statement that does essentially nothing. Any ideas on that?

5. Urs (us) Schwarz replied on October 20th, 2006 at 20:37 UTC :
   

   SNIP doug not only having lost a shock of hair…

   firstly, the loop uses a var BITS, which is NOT pre-allocated (as properly shown in the alternative[?] section) – hence, the demo may broadcast a very false message… customers beware…

   secondly, the movie can be done (so much!) better…

   just a pedestrian note with a :-)
   us

6. Ben replied on October 22nd, 2006 at 22:46 UTC :
   

   That is awesome! I never knew this existed! Its cooler then those Progress Bars!

7. Doug replied on October 23rd, 2006 at 11:47 UTC :
   

   BITS indeed is not pre-allocated in the first block of code. That is part of the problem with the original code. These errors in the code are intentional, that is the point of the demonstration. Even with pre-allocation, the new code is a great improvement. In a longer demo, this pre-allocation error is found with the m-lint feature of the profiler.

   Glad to see people are looking closely.

8. Doug replied on October 24th, 2006 at 09:41 UTC :
   

   Andreas,

   I did not know the answer, so I went to development and got this answer:

   “What the customer is seeing is not a bug but a side effect of how the JIT [Just In Time accelerator] operates. Often at the end of loops it must transfer control back to the interpreter which is an expensive operation. The “end” statements are usually where this time ends up getting assigned when profiling programs like this.”

   Now we all know!
   Doug

9. Gopakumar replied on November 17th, 2006 at 10:50 UTC :
   

   Thanks for the videos Doug. Appreciate it :)

10. srikanth kadiyala replied on December 15th, 2006 at 09:51 UTC :
    

    “I really gained some knowledge from this video to find the time taken by the functions and variables”

    Thanks for the videos

11. Nati replied on December 25th, 2006 at 04:12 UTC :
    

    Hi Doug !
    I’m using the profiler a lot. I want to know if there is a way to profile a mex file.The profiler treats it like a built in function.
    Thank’s a lot.
    Nati

12. Doug replied on January 9th, 2007 at 14:50 UTC :
    

    Nati,

    If you want visibility into the C code in a mex file, you will need to use the debuging capabilities of your external development environment.

    Doug

13. Luxus replied on February 3rd, 2007 at 02:05 UTC :
    

    Great and excellent article t’s realy helpful. Thanks again.

14. Ramjee Prasad Gupta replied on February 9th, 2007 at 04:45 UTC :
    

    Thanks for video

15. torben replied on March 23rd, 2007 at 10:14 UTC :
    

    Excellent article it’s realy helpful, keep up the good work!

16. gutschein replied on March 27th, 2007 at 10:12 UTC :
    

    Great articles. Very interesting.

17. vincent replied on March 27th, 2007 at 14:33 UTC :
    

    your vedio was very useful

    i was also thinking that if you can give more examples of how to use matlab will help the world.

18. Morten L. Jørgensen replied on May 18th, 2007 at 12:06 UTC :
    

    My profiler returns something like 9246494268.503 seconds of total time and self time for some functions, this is odd since i only ran the simulation for 8 seconds :-). What am I doing wrong?

19. Robert replied on June 26th, 2007 at 06:39 UTC :
    

    A great and useful viedeo.
    A big thank!

20. Thijs replied on August 14th, 2007 at 08:59 UTC :
    

    I’am experiencing the same problem as Morten L. Jorgensen.
    Is their anyone familiar with this problem, and its solution?

21. Thijs replied on August 14th, 2007 at 09:15 UTC :
    

    The following bug (AMD dual core) was the cause:

    http://www.mathworks.com/support/bugreports/details.html?rp=310027

    A workaround is also described.
    This is bug solved in R2007a.

22. Family replied on October 7th, 2007 at 22:12 UTC :
    

    A great and useful viedeo.
    A big thank!

23. Michael Israel replied on October 11th, 2007 at 08:31 UTC :
    

    Hi,

    Great video,
    actually I have a problem.
    The profiler shows some “if” statements that
    take a lot of time, (simple ifs like if a == 1), other ifs
    and ends take 6 seconds.

    About end statements, I understand from previous guys
    but why if statements are so slow, I just want to know if it is some kind of a bug or it is a MATLAB limitation ?

    Hope to get an answer,
    Thanks

    [comment reformatted for clarity- Doug]

24. Doug replied on October 11th, 2007 at 08:47 UTC :
    

    Michael,

    I just tested this in the manner you described it. I saw no slowdown on the if statements. Please send the code into tech support and we will see what they can do for you.

    Thanks,
    Doug

25. Michael Israel replied on October 11th, 2007 at 08:53 UTC :
    

    Thanks for fast reply,
    How can I do it via email?

    [Edited for clarity- Doug]

26. Doug replied on October 11th, 2007 at 09:19 UTC :
    

    Contact support at:

    http://www.mathworks.com/support/

    support@mathworks.com

27. asim replied on December 27th, 2007 at 17:04 UTC :
    

    Thank you very much..I have gone through most of your videos and all are extrmely helpful.

28. Daniel replied on February 13th, 2008 at 02:32 UTC :
    

    great haircut, great picture Doug!

29. adnyana replied on February 19th, 2008 at 05:02 UTC :
    

    Mr. Doug, i’ve run my code on profiler, but nothing i can do after i find line code where the most time spent. that line code is ‘ismember’. because i don,t know what the other function work like that but faster.

    i use that function to check if data from one set is member of other set.

    could you help me Mr

    best regard

    adnyana

30. Billigflug Bali replied on July 30th, 2008 at 09:53 UTC :
    

    Oh yes. Very useful vid! Thank you. And thanks for telling us how you made the video, I was searching for such a tool, too.

31. peter replied on March 15th, 2013 at 06:04 UTC :
    

    nice haircut!

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These postings are the author's and don't necessarily represent the opinions of MathWorks.