Doug's MATLAB Video Tutorials

July 6th, 2010

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.

14:19 UTC | Posted in Format: Video, Level: Basic | Permalink | 11 Comments »

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11 Responses to “Debugging is faster with save and load”

1. Oscar replied on July 6th, 2010 at 18:06 UTC :
   

   Pretty simple but heaven help me if it ever occurred to me. I guess that is why you wear that pimp hat.

2. dhull replied on July 6th, 2010 at 18:33 UTC :
   

   @Oscar,

   It comes from years of debugging other people’s code… I do miss that hat, leather shrinks in the sun apparently! :(

   -Doug

3. Daniel Armyr replied on July 7th, 2010 at 07:05 UTC :
   

   Nifty and short. I like it. (Both the hat and the video).
   –DA

4. the cyclist replied on July 7th, 2010 at 12:41 UTC :
   

   A closely related technique to this one is using “cell mode,” which is one of my favorite MATLAB desktop innovations ever. Create a cell around the really slow part, and then another cell around the buggy part. Run the slow cell first. Then you can repeatedly run and debug the buggy part, without running the slow part over and over again.

5. dhull replied on July 7th, 2010 at 15:11 UTC :
   

   @cyclist

   I like that method also, but I have one concern with it. It is possible to change the initial state in the troublesome cell. Then any changes that you make to the code might not have the intended effect.

   If you are confident this is not the case, then the cell mode technique is even faster to implement.

   Doug

6. Joshua Arnott replied on July 7th, 2010 at 15:29 UTC :
   

   When I’m doing this instead of commenting out the slow code (even with %{ %} group comments) or keeping it in a different cell, I’ll often move the cell I’m working on into an entirely seperate file, with a load of the “known good run” as Doug does. That way I keep the main codebase clean (as it ever is) and can save “experiments” elsewhere before merging.

7. Jotaf replied on July 7th, 2010 at 18:46 UTC :
   

   This is a technique I use often; many times I have some code to pre-process raw data (ie, extract features from a video), and it’s not necessary to repeat it all the time.

   Instead of commenting/uncommenting the whole code, I use a simple flag that is easy to toggle by commenting/uncommenting (Ctrl+R, Ctrl+T), and the following structure:

   % recalculate_whatever = true;
   recalculate_whatever = false;
   
   if recalculate_whatever
     %long calculation
     %...
     save whatever data1 data2 ...
   else
     load whatever data1 data2 ...
   end
   
   %code that uses data1, etc
   %...
   

8. dhull replied on July 7th, 2010 at 18:48 UTC :
   

   @Jotaf

   That is an excellent plan. Reminds me of something I do like having a variable “Verbose” and setting up some debugging DISP commands inside if blocks throughout the code.

   Thanks,
   Doug

9. Rodney Thomson replied on July 8th, 2010 at 02:42 UTC :
   

   @dhull

   What I have done in the past is use a global variable ‘VERBOSE’ and have a debugging function that mirrors fprintf syntax (which I call log_debug to match our C++ code):

   %——————————-
   function log_debug(varargin)
   global VERBOSE

   if (VERBOSE)
   fprintf(1, varargin{:});
   end
   end
   %——————————-

   Example usage:
   >> whos
   >> log_debug(‘One %d two %d three %d\n’, 1, 2, 3)
   >> global VERBOSE
   >> VERBOSE = true;
   >> log_debug(‘One %d two %d three %d\n’, 1, 2, 3)
   One 1 two 2 three 3
   >>

10. dhull replied on July 8th, 2010 at 13:56 UTC :
    

    @Rodney,

    That reminds me, I had a DDISP command that sourced a global VERBOSE. If verbose was one, the DDISP would DISP whatever I gave DDISP, otherwise it would do nothing.

    Doug

11. Timberland Boots UK replied on September 27th, 2010 at 03:52 UTC :
    

    Pretty good post. I just stumbled upon your blog and wanted to say that I have really enjoyed reading your blog posts. Any way I’ll be subscribing to your feed and Timberland Boots UKI hope you post again soon.

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