Good programming practice...

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!

[Michael Leung]

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.

[Steven]

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.

Answer 1

[Daniel Shub]

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]

Elements of Matlab Style is great

Answer 2

[Jake Bolanski]

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]

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

Answer 3

[Jan]

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.

[Daniel Shub]

I wish I could vote many many times.

[Bjorn Gustavsson]

"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!

Answer 4

[Fangjun Jiang]

Where do you want to start? I'll add as I come up with some.

• pre-allocate large size variables using zeros(), cell()

Answer 5

[Jan]

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]

@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.

Answer 6

[Jan]

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]

Even the best sometimes do it:

http://blogs.mathworks.com/loren/2009/06/16/rooting-around-in-matlab-part-2/

Answer 7

[Daniel Shub]

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]

I wish, that you do *not* come to Answers, but proceed to the above two links immediately... But I vote the helpful links +1.

Answer 8

[Daniel Shub]

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')

[Jan]

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]

@jan you are correct, catching the output of load is an important piece of good practice.

Answer 9

[Jan]

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]

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.

Answer 10

[Jan]

Include a check of number and type of inputs if all functions.

This will cost several seconds runtime, but will save hours of debugging.

Answer 11

[Jan]

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.

Answer 12

[Jan]

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

Answer 13

[Daniel Shub]

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]

+1. I remember reading Doug's post. That's a good one.

Answer 14

[Daniel Shub]

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/

Answer 15

[Raviteja]

I got good help from matlab datasheets for matlab programming tips

http://www.mathworks.in/help/pdf_doc/matlab/programming_tips.pdf

[mohammad]

@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]

@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.

[Walter Roberson]

@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

[mohammad]

@Jan I just generalize a byword to MATLAB, take it easy for a beginner like me

[Walter Roberson]

@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]

@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)

[Jan]

@Walter: You do think that the clock is a source of non-determinism. Isn't this heresy?

[Walter Roberson]

@Mohammad: http://www.flickr.com/photos/gothamoddisee/216748915/

(Be sure to read the caption)

[mohammad]

Nice, thanks Walter

[mohammad]

I use this: www.google.com/bookmarks

but it's to be nice if here has itself Bookmarks

Answer 16

[Steven]

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]

@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.