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Raviteja

Good programming practice...

Raviteja on 22 Sep 2011
Latest activity Reply by Daniel Shub on 27 Jan 2012

Hello all,
Please explain good MATLAB programming practice methods. It will help to the guys who are new to programming like me.
Previously I used
for i=1:10
after following some suggestions from this answers pages I learnt to use
for i1=1:100
This is the good way to write programs.
Like this, as a professional programmer, please mention some good programming practice techniques.
It will useful to all!

40 Comments

Daniel Shub
Daniel Shub on 27 Jan 2012
It is only fair that if I plug Doug's blog, I should plug Loren's blog also:
http://blogs.mathworks.com/loren/2012/01/13/best-practices-for-programming-matlab/
Daniel Shub
Daniel Shub on 20 Oct 2011
Surprised Doug didn't chime in with his blog post: http://blogs.mathworks.com/videos/2010/03/08/top-10-matlab-code-practices-that-make-me-cry/
Fangjun Jiang
Fangjun Jiang on 20 Oct 2011
+1. I remember reading Doug's post. That's a good one.
Steven
Steven on 19 Oct 2011
However, the difference seems to be indistinguishable considering a certain precision whatever the number of repetitions.
tic;
for i1 = 1:100000
x = sin(i1);
end
toc
Elapsed time is 0.003597 seconds.
tic;
for i = 1:100000
x = sin(i);
end
toc
Elapsed time is 0.003569 seconds.
Jan
Jan on 27 Jan 2012
@Steven: You have posted this detail 3 times in this thread. Please consider, that the runtime is not affected by the length of the name of the variable, because internally the variable is accessed by a memory pointer taken from a lookup-table. This lookup-table is created when the function is loaded the first time only.
Steven
Steven on 19 Oct 2011
However, the difference seems to be indistinguishable considering a certain precision.
tic;
for i1 = 1:100000
x = sin(i1);
end
toc
Elapsed time is 0.003597 seconds.
tic;
for i = 1:100000
x = sin(i);
end
toc
Elapsed time is 0.003569 seconds.
Jan
Jan on 23 Sep 2011
This is a list of helpful links: http://www.ee.columbia.edu/~marios/matlab/matlab_tricks.html
E.g. this is exhaustive: http://www.ee.columbia.edu/~marios/matlab/MatlabStyle1p5.pdf
Jan
Jan on 23 Sep 2011
Read the FAQ
It is very likely, that the questions, which concern other users frequently, do concern you also. It is very efficient to profit from the mistakes of others, instead to implement them by your own.
Bjorn Gustavsson
Bjorn Gustavsson on 23 Sep 2011
"It is very efficient to profit from the mistakes of others, instead to implement them by your own." was one of the funniest (sadly fun, funily said) statements I've come across this week!
Daniel Shub
Daniel Shub on 23 Sep 2011
I wish I could vote many many times.
Jan
Jan on 23 Sep 2011
Read the tips for program development in the dokumentation:
http://www.mathworks.de/help/techdoc/matlab_prog/f10-60481.html
And if you are on the way, read the rest of the documentation also, at least the "Getting Strarted" chapters.
Daniel Shub
Daniel Shub on 23 Sep 2011
Use the functional form of load and save, and almost every other function except maybe help and doc
instead of
load filename.mat
use
data = load('filename.mat')
Daniel Shub
Daniel Shub on 23 Sep 2011
@jan you are correct, catching the output of load is an important piece of good practice.
Jan
Jan on 23 Sep 2011
Same for SAVE.
And catch the output: Data = load(FileName), otherwise you could find unexpected variables in your workspace like "max", which will shadow existing functions to your surprise. See http://www.mathworks.com/matlabcentral/answers/16484-good-programming-practice#answer_22299
Daniel Shub
Daniel Shub on 23 Sep 2011
Come to Answers before using global or eval. There is almost always a better way to do it.
http://matlab.wikia.com/wiki/FAQ#Why_is_it_advised_to_avoid_using_the_.22eval.22_function.3F
http://www.mathworks.co.uk/support/tech-notes/1100/1103.html
Jan
Jan on 23 Sep 2011
I wish, that you do *not* come to Answers, but proceed to the above two links immediately... But I vote the helpful links +1.
Daniel Shub
Daniel Shub on 23 Sep 2011
I suggest developing a coding "style." Some good places to start are given in the FAQ:
http://matlab.wikia.com/wiki/FAQ#Where_can_I_find_MATLAB_Style_Guides_or_Coding_Standards.3F
I also would consider this book reviewed by Loren
http://blogs.mathworks.com/loren/2011/02/10/book-review-the-elements-of-matlab-style/
although I should say I have not looked at it yet. It is on my list of things to do.
K E
K E on 26 Jan 2012
Elements of Matlab Style is great
Raviteja
Raviteja on 23 Sep 2011
I got good help from matlab datasheets for matlab programming tips
http://www.mathworks.in/help/pdf_doc/matlab/programming_tips.pdf
mohammad
mohammad on 24 Sep 2011
I use this: www.google.com/bookmarks
but it's to be nice if here has itself Bookmarks
mohammad
mohammad on 23 Sep 2011
Nice, thanks Walter
Walter Roberson
Walter Roberson on 23 Sep 2011
@Mohammad: http://www.flickr.com/photos/gothamoddisee/216748915/
(Be sure to read the caption)
Jan
Jan on 23 Sep 2011
@Walter: You do think that the clock is a source of non-determinism. Isn't this heresy?
mohammad
mohammad on 23 Sep 2011
@Walter there are many useful questions here if I add tag to all of those topics, how could I remember tags or even subjects? (for example for more than 50 questions)
Walter Roberson
Walter Roberson on 23 Sep 2011
@Jan: MATLAB has access to the clock and other sources of non-determinism. And there are some pretty strong theorems about indeterminacy in the exact order of parallel access, I seem to recall.
mohammad
mohammad on 23 Sep 2011
@Jan I just generalize a byword to MATLAB, take it easy for a beginner like me
Walter Roberson
Walter Roberson on 23 Sep 2011
@Mohammad: you could add a "tag" to the topic that you can remember, and then to find the topic again, you could search by tags.
Suppose, for example, you added the tag best-practices to this topic. Then, to find it again, in the search box, you would enter the query
tag:best-practices
Jan
Jan on 23 Sep 2011
@Mohammed: You've said "With MATLAB impossible is impossible".
MATLAB can calculate primitive recursive functions only.
You have to call Java to get more, e.g. indeterminism or a uitable.
mohammad
mohammad on 23 Sep 2011
@Walter You are right, I did that and deleted that answer
but i can't access when I am in university or other places
Jan
Jan on 22 Sep 2011
Include a check of number and type of inputs if all functions.
This will cost several seconds runtime, but will save hours of debugging.
Jan
Jan on 22 Sep 2011
Do not start a script or function by:
clear all
This removes all loaded functions from the memory. Reloading them will need a lot of time such that a program can be 100 times slower in a not so unlikely worst case.
I admit that a clear or the equivalent clear variables can help to detect crude typos in names of a variable, if this variable is existing before the script. But this is a really rare case and if a function is used, MLint detects this much better.
But there is a frightening large number of codes starting with clear all. I assume this is recommended in some tutorials which have been written without deeper insight into MATLAB.
Daniel Shub
Daniel Shub on 20 Oct 2011
Even the best sometimes do it:
http://blogs.mathworks.com/loren/2009/06/16/rooting-around-in-matlab-part-2/
Jan
Jan on 22 Sep 2011
Avoid overloading builtin functions. It happens very often, that a user creates a variable called "max" and is surprised that the MAX function does not work anymore:
max = 19;
... 100 lines later:
B = max(1:10)
??? Index exceeds matrix dimensions.
A confusing but correct error message!
Jan
Jan on 26 Jan 2012
@Steven: As you've found out, longer symbols do not need more time (as long as the lookup table is not poluted by EVALs). While runtime is not a problem, debug time is. "B=max(1:10)" is confusing.
Jan
Jan on 22 Sep 2011
Use English for comments and the help text. Although you might assume, that you will never share the code, even a discussion in this forum is much harder, if all variables and descriptions are in Italian.
Walter Roberson
Walter Roberson on 23 Sep 2011
This one I cannot really agree with. It trades the possibility that one might want to share a section of the code in Answers or CSSM, against the near certainty that the code will need to be easily understandable by other people in one's workplace.
There are also locations were writing the comments and help text in English would violate various language preservation laws.
Fangjun Jiang
Fangjun Jiang on 22 Sep 2011
Where do you want to start? I'll add as I come up with some.
  • pre-allocate large size variables using zeros(), cell()
Jake Bolanski
Jake Bolanski on 22 Sep 2011
It's always good to comment in front of your code so that you won't have trouble remembering why you did what you did. It also helps others recognize your code and what you're doing.
Jan
Jan on 22 Sep 2011
I agree. If you want to share your code, or do this ever in the future, it is a good idea to use the standard comment style of Matlab:
function [Output, ...] = Fcn(Input, ...)
% H1 line
% Help text
% [Output, ...] = Fcn(Input, ...)
% ...
% Date, author
Michael Leung
Michael Leung on 22 Sep 2011
You are right! i is undesirable for the loop variable as matlab treats i as the complex number, sqrt(-1).
I personalty use ii and jj for my loops, but as long as its not the lonesome "i" it will speed up your code.

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