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Jim Riggs
Last activity on 4 Mar 2024

Is Walter Roberson a real person, or is he some kind of Matlab AI robot?

Just curious!

Stephen23
Last activity on 10 Apr 2024

TUTORIAL: Why Variables Should Not Be Named Dynamically (eval)

Summary:

Dynamically accessing variable names can negatively impact the readability of your code and can cause it to run slower by preventing MATLAB from optimizing it as well as it could if you used alternate techniques. The most common alternative is to use simple and efficient indexing.

Explanation:

Sometimes beginners (and some self-taught professors) think it would be a good idea to dynamically create or access variable names, the variables are often named something like these:

matrix1, matrix2, matrix3, matrix4, ...
test_20kmh, test_50kmh, test_80kmh, ...
nameA, nameB, nameC, nameD,...

Good reasons why dynamic variable names should be avoided:

There are much better alternatives to accessing dynamic variable names:

Note that avoiding eval (and assignin, etc.) is not some esoteric MATLAB restriction, it also applies to many other programming languages as well:

MATLAB Documentation:

If you are not interested in reading the answers below then at least read MATLAB's own documentation on this topic Alternatives to the eval Function, which states "A frequent use of the eval function is to create sets of variables such as A1, A2, ..., An, but this approach does not use the array processing power of MATLAB and is not recommended. The preferred method is to store related data in a single array." Data in a single array can be accessed very efficiently using indexing.

Note that all of these problems and disadvantages also apply to functions load (without an output variable), assignin, evalin, and evalc, and the MATLAB documentation explicitly recommends to "Avoid functions such as eval, evalc, evalin, and feval(fname)".

The official MATLAB blogs explain why eval should be avoided, the better alternatives to eval, and clearly recommend against magically creating variables. Using eval comes out at position number one on this list of Top 10 MATLAB Code Practices That Make Me Cry. Experienced MATLAB users recommend avoiding using eval for trivial code, and have written extensively on this topic.

Matt Tearle
Last activity on 6 Mar 2023

MATLAB poems -- let's hear 'em!

Inspired by Chad Greene's " MATLAB jokes or puns " thread, and in celebration of 15 years of the MathWorks Community site, does anyone out there want to share their poetic creativity? Limericks, haiku, sonnets... Go!

And to start off, my (slightly off-topic) submission on Chad's thread:

There was an old math guy called Cleve
who, while teaching, a pipe-dream conceived:
    of a language so clean
    you can say what you mean!
From our suffering we've all been relieved.

Walter Roberson
Last activity on 30 Jul 2024

[DISCONTINUED] MATLAB Answers Wish-list #4 (and bug reports)

Edit: due to the increasing size of this thread, it is continued here.

What should you post where?

Wishlist threads (#1 #2 #3 #4 #5 #6): bugs and feature requests for Matlab Answers

Frustation threads (#1 #2): frustations about usage and capabilities of Matlab itself

Missing feature threads (#1 #2): features that you whish Matlab would have had

Next Gen threads (#1): features that would break compatibility with previous versions, but would be nice to have

This topic is for features you would like to see for the MATLAB Answers facility itself, and also for bug reports about the MATLAB Answers facility.

This topic is the follow on to the first Wish-list for MATLAB Answer sections and second MATLAB Answers Wish-list #2 (and bug reports). Those grew large enough to become unwieldy; and Mathworks has made enough changes to make a number of the past points no longer of relevance. More recently there was the limited purpose New design of the forum - grey on white which turned into a bug and wish list; I have renamed that for continuity.

I suggest one wish (or bug report) per answer, so that people can vote their wishes.

372

bio lim
Last activity on 25 Mar 2024

Experts of MATLAB, how did you learn? Any advice for beginner/intermediate users?

The community is very helpful, yet I feel really powerless that I cannot find the appropriate way to code, nor find the problems with the codes I have written. I have read numerous books on MATLAB, mostly related with science and engineering applications. Any advice to improve would be greatly appreciated. Thanks.

Chad Greene
Last activity on 12 Sep 2023

Matlab jokes or puns

Are there any good Matlab jokes? I don't mean why or any other Easter eggs, I mean good jokes involving Matlab. Actually, that bar may be a bit too high. Any jokes, good or bad, let's hear 'em.

632

Jan
Last activity on 25 Feb 2020

[DISCONTINUED] New design of the forum - grey on white / wish list #3 / bug reports

NOTE: this discussion is continued at MATLAB Answers Wish-list #6 (and bug reports)

I've opened MATLAB Answers this morning and found the new design.

The field for typing the "Body" does not consider the font settings of my browser anymore, such that my preference of sans-serif fonts is ignored. In addition the text color is a medium gray, which is hard to read for me due to the too light contrast.

Blank lines in the code let two separate code boxes appear. This makes almost all code, I've posted in the forum, invalid. It has been discussed repeatedly, that blank lines in the code confuse the indentation of the display in the forum and that this is a really bad idea. But instead of improving this, it is made severely worse now.

The new design contains even more white space, such that standard questions cannot be answered without extensive vertical scrolling. It is a very bad drawback, that I cannot see the question while I type the answer.

There is still no suggestion to use a proper code formatting, such that I have to spend 20% of my forum time typing corresponding comments as before.

But I'm coming back to the most important problem for me: It is a physical problem for me to read the low contrast grey on white text. Does anybody know a tweak or CSS trick to increase the readability?

TMW, please take into account that this new design is physically hard to read for people without young and 100% perfect eyes. This is very annoying for me.

Splitting code blocks at white lines is simply a bug. I cannot imagine why this error has not been detected before the new design has been published. The argument, that TMW is extremely conservative with changes in the forum to ensure a stability does not convince me anymore.

[EDITED] The box around the thread, the preview box, the boxes for preformatted text and code have a grey background now. So some text is even medium grey on light grey.

I'd be glad if the designers refocus on the purpose of the forum. Whatever this purpose might be, the optical reception of the characters is fundamental.

118

Sven
Last activity on 7 Jul 2023

What's on your personal MATLAB to-do list?

What MATLAB tools or functions have you been thinking about making but haven't quite gotten around to it?

It can be something specific to your work if you'd like, but it's preferably:

the kind of tool or task that we don't really expect in the next MATLAB release (ie., not a frequent entry in a MATLAB wishlist)
something that would be useful to you and (hopefully) others if it existed.
something that could conceivably be made by people(s) in the user community

Think of it maybe as a file exchange wishlist.

Votes for good ideas . I guess you'll get more votes if it's an idea others want to see made as well.

Probably no single accepted answer, but it would be nice to see what people have thought about and maybe we can bring a few ideas to fruition (or find that someone's already done it)

For example:

I've been wanting to write an object-oriented replacement for the NURBS toolbox which is a great toolbox but is very unwieldy to use.

Oleg Komarov
Last activity on 27 Jul 2023

Spellcheck functionality in MATLAB editor

I would like to receive your feedback:

would you find useful to have spellcheck built into the MATLAB Editor?

(Consider also an associated toggle, positioned somewhere in the Editor, that would enable/disable the spellcheck for selective use)

Lately, I am writing many quick analyses for publish() and I find that first publishing to MS Word (to check the spelling) and then re-publishing to .html, after manual corrections, disrupts the working.

IMHO, the idea to include spellcheck into the editor would be consistent with the renewed visibility of the PUBLISH tab.

Walter Roberson
Last activity on 25 Feb 2020

[DISCONTINUED] MATLAB Answers Wish-list #2 (and bug reports)

NOTE: this discussion is continued at MATLAB Answers Wish-list #6 (and bug reports)

This topic is for features you would like to see for the MATLAB Answers facility itself, and also for bug reports about the MATLAB Answers facility.

This topic is the follow on to the earlier Wish-list for MATLAB Answer sections. That topic grew large enough to become unwieldy; and Mathworks has made enough changes to make a number of the past points no longer of relevance. There was also a more limited purpose <http://uk.mathworks.com/matlabcentral/answers/216662-new-design-of-the-forum-grey-on-white-wish-list-3-bug-reports

I suggest one wish (or bug report) per answer, so that people can vote their wishes.

227

Raviteja
Last activity on 27 Jan 2012

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!

Oleg Komarov
Last activity on 9 Dec 2021

Greek alphabet and latex commands [not a question]

Capital letters are obtained by capitalizing the LaTeX command for the lowercase version. Capital letters in grey are exceptions which have no LaTeX commands. For example, to produce a capital chi simply type X (this also applies for the lowercase omicron).

When two versions of the lowercase letter are available, a var prefix can be added to obtain the second version. For example, the two versions of epsilon are \epsilon and \varepsilon.

--------------------------------------------------------------------------------------------------------------------------------------------------------

The code used to generate the table:

greeks = ...
{'ALPHA'      'A'         '\alpha'
 'BETA'       'B'         '\beta'
 'GAMMA'      '\Gamma'    '\gamma'
 'DELTA'      '\Delta'    '\delta'
 'EPSILON'    'E'         {'\epsilon','\varepsilon'}
 'ZETA'       'Z'         '\zeta'
 'ETA'        'H'         '\eta'
 'THETA'      '\Theta'    {'\theta','\vartheta'}
 'IOTA'       'I'         '\iota'
 'KAPPA'      'K'         '\kappa'
 'LAMBDA'     '\Lambda'   '\lambda'
 'MU'         'M'         '\mu'
 'NU'         'N'         '\nu'
 'XI'         '\Xi'       '\xi'
 'OMICRON'    'O'         'o'
 'PI'         '\Pi'       {'\pi','\varpi'}
 'RHO'        'P'         {'\rho','\varrho'}
 'SIGMA'      '\Sigma'    {'\sigma','\varsigma'}
 'TAU'        'T'         '\tau'
 'UPSILON'    '\Upsilon'  '\upsilon'
 'PHI'        '\Phi'      {'\phi','\varphi'}
 'CHI'        'X'         '\chi'
 'PSI'        '\Psi'      '\psi'
 'OMEGA'      '\Omega'    '\omega'};
h = figure('units','pixels','pos',[300,100,620,620],'Color','w');
axes('units','pixels','pos',[10,10,600,600],'Xcol','w','Ycol','w',...
     'Xtick',[],'Ytick',[],'Xlim',[0 6],'Ylim',[0,4]);

% Loop by column and row

for r = 1:4
    for c = 1:6
        el = (r-1)*6 + c;
        % Title
        text(c-0.5,5-r,greeks{el,1},'Fonts',14,'FontN','FixedWidth',...
            'Hor','center','Ver','cap')
        % Color cap latter in grey or black
        if strcmp(greeks{el,2}(1),'\')
            clr = [0, 0, 0];
        else
            clr = [0.65, 0.65, 0.65];
        end
        % Cap letter
        text(c-0.5,4.87-r,['$\rm{' greeks{el,2} '}$'],'Fonts',40,...
            'Hor','center','Ver','cap','Interp','Latex','Color',clr)
        % Lowercase letter/s (if two variants) 
        if iscell(greeks{el,3})
            text(c-0.75,4.48-r,['$' greeks{el,3}{1} '$'],'Fonts',20,...
                'Hor','center','Interp','Latex')
            text(c-0.25,4.48-r,['$' greeks{el,3}{2} '$'],'Fonts',20,...
                'Hor','center','Interp','Latex')
            % Latex command
            text(c-0.5,4.3-r,['\' greeks{el,3}{1}],'Fonts',12,'FontN','FixedWidth',...
            'Hor','center','Ver','base')
        else
            text(c-0.5,4.48-r,['$' greeks{el,3} '$'],'Fonts',20,...
                'Hor','center','Interp','Latex')
            text(c-0.5,4.3-r,['\' greeks{el,3}],'Fonts',12,'FontN','FixedWidth',...
            'Hor','center','Ver','base')
        end
    end
end

% Print to pdf

export_fig greeks.pdf

The link to export_fig.

And here is the link to the pdf on scribd: http://www.scribd.com/doc/159011120/Greek-alphabet-in-latex

Oleg Komarov
Last activity on 8 Mar 2023

TUTORIAL: how to format your question with markup

[INDEX]

--------------------------------------------------------------------------------------------------------------------------------------

[MOTIVATION]

Why should we use markups in the body of our questions?

The answer is a question: which of the two versions is more likely to be understood in a glimpse and has more chances to be answered by our readers?

< Consider the following question >

I have a vector of weights W=[10,20,30,50,23434,1,2.4,2] and a matrix A=rand(100,8) and I would like to find the row-wise weighted sum of A. I am proceeding in the following way: B=zeros(size(A)); for c=1:numel(W) B(:,c)=A(:,c)*W(c); end B=sum(B,2); Somehow I get huge numbers can you please help?

< Now, consider its formatted version >

I have a vector of weights W = [10,20,30,50,23434,1,2.4,2] and a matrix A = rand(100,8) and I would like to find the row-wise weighted sum of A.

I am proceeding in the following way:

B = zeros(size(A));
for c = 1:numel(W)
    B(:,c) = A(:,c)*W(c);
end
B = sum(B,2);

Somehow I get huge numbers can you please help?

--------------------------------------------------------------------------------------------------------------------------------------

[AKNOWLEDGMENTS]

In alphabetical order by nickname, thanks for their suggestions to:

Walter Roberson

--------------------------------------------------------------------------------------------------------------------------------------

[LOG]

06 Aug 2011, 13:17 BST - created and added boldface.gif
06 Aug 2011, 14:59 BST - added italic.gif
06 Aug 2011, 18:58 BST - added index section
07 Aug 2011, 00:03 BST - added code.gif and tutorial series section
07 Aug 2011, 01:50 BST - added monospaced.gif, numlist.gif, bullist.gif and hyperlink.gif
13 Aug 2011, 14:27 BST - added motivation section
18 Aug 2011, 01:44 BST - added aknowledgments section and link to wish-list

--------------------------------------------------------------------------------------------------------------------------------------

[TUTORIAL Series]

How to ask a question (on Answers) and get a fast answer

Do not forget to read the Markup help (located on the top-right corner of the Body pane)

Vote on Wish-list for MATLAB Answer sections my post if you think that a tutorial section on top of Answers could be useful.

Jason
Last activity on 16 Dec 2020

Best way(s) to master MATLAB?

Now, I am still a novice when it comes to programming. I believe MATLAB is definitely a great programming tool, one that I can play with, particularly, when I have free time.

I would love to hear from all answerers, what are the ways that can make one proficient in this field?

Walter Roberson
Last activity on 14 Jul 2022

MATLAB in unexpected places

This topic is for unexpected or bizarre or humorous references to MATLAB. Specific citations would be appreciated.

Paulo Silva
Last activity on 10 May 2024

What matlab easter eggs do you know?

Please post the easter eggs that you have found so far if they aren't already posted by someone else.

Let's try to make a good Matlab easter egg list because it seems that there isn't one.

What should be posted:

Unexpected but intentional behaviour
Special things that the programmers left for us to discover
Extra code inside a function that can be used for other purposes
Hidden pictures and audio clips

What shouldn't be posted:

Repeated Easter Eggs, if someone already posted it please don't repeat
Bugs in functions that cause trouble and might be fixed in later versions
Matlab games that come with the program unless they aren't mentioned in the documentation (the games are in the other demos, try the xpbombs and fifteen, you can even see the code for both games)

Paulo Silva
Last activity on 14 Aug 2023

What is missing from MATLAB?

I'm curious, is there something you wish to do with MATLAB but you can't, maybe something you can do with other similar software but can't with MATLAB?

For new entries, please use the follow-up thread here. Please do not post new answers in this thread.

470

amit jain
Last activity on 2 Jun 2023

How to learn MATLAB

What is the best way to learn MATLAB at home without a tutor?