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Rik
Rik
Last activity il 17 Set 2024

What frustrates you about MATLAB? #2

Similar to what has happened with the wishlist threads (#1 #2 #3 #4 #5), the "what frustrates you about MATLAB" thread has become very large. This makes navigation difficult and increases page load times.
So here is the follow-up page.
What should you post where?
Wishlist threads (#1 #2 #3 #4 #5): 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
@anyone posting a new thread when the last one gets too large (about 50 answers seems a reasonable limit per thread), please update this list in all last threads. (if you don't have editing privileges, just post a comment asking someone to do the edit)
Even
Even
Last activity il 23 Lug 2023

Problem 44951. Verify Law of Large Numbers

If a large number of fair N-sided dice are rolled, the average of the simulated rolls is likely to be close to the mean of 1,2,...N i.e. the expected value of one die. For example, the expected value of a 6-sided die is 3.5.
Given N, simulate 1e8 N-sided dice rolls by creating a vector of 1e8 uniformly distributed random integers. Return the difference between the mean of this vector and the mean of integers from 1 to N.
function dice_diff = loln(N)
A=randi([1,N],1e8,1)
M=mean(A)
B=1:N
m=mean(B)
dice_diff =abs(M-m);
end
Here is my code, but it can't work out as it needs too long time to creat A.
In problem 16 I used the following solution:
function b = nearZero(a)
b = max(a(imdilate(a == 0, [1 1 1])));
end
It is working pretty well on mathlab but when I submit my answer to cody, the following error is generated:
Undefined function 'imdilate' for input arguments of type 'double'.
Error in nearZero (line 2)
b = max(a(imdilate(a == 0, [1 1 1])));
Error in Test1 (line 3)
assert(isequal(nearZero(a),b))
In number 5, its written that the correct answer is c = 1 but the secomnd person has more change than the first person, therefor the correct answer should be 2.Likewise in number 6.
Hi, I'm trying to solve this problem but I'm getting an error so far.
Problem:
Given a vector a, find the number(s) that is/are repeated consecutively most often. For example, if you have
a = [1 2 2 2 1 3 2 1 4 5 1]
The answer would be 2, because it shows up three consecutive times
What I've written so far (not done):
a = [1 2 2 2 1 3 2 1 4 5 1];
[x,y] = size(a);
counter = zeros(1,10);
if x == 1
for i=1:1:y
if a(i) == a(i+1)
counter(a(i)) = counter(a(i))+1
end
end
else
for i=1:1:x
if a(i) == a(i+1)
counter(a(i)) = counter(a(i))+1
end
end
end
But it says "error" in the line of "if a(i) == a(i+1)". I noticed that it creates a variable called "i" which value is 11, but it should create a vector from 1 to 11. What's wrong here?
I know my solution might not be in the right direction or something, but please don't tell me anything!
Thanks in advance
Jan
Jan
Last activity il 4 Ott 2024

Table of Matlab release features

After reading Rik's comment I looked for a list of Matlab releases and their corresponding features. Wiki: Matlab contains an exhaustive list, but what about having a lean version directly in the forum?
If this is useful, feel free to expand the list and to insert additions. Thank you.
Rik
Rik
Last activity il 4 Nov 2022

How to create a GUI

There are multiple ways to create a graphical user interface (GUI) in Matlab. Which method is the best depends on multiple factors: the complexity of the project, to what extent it should be a long-term solution, on what releases your GUI should work, your available time, your skill level, and probably other factors I'm forgetting.
To keep the thread clear I'll attempt to provide a short outline a few ways in this question, and leave the details for the answers. (@anyone with editing privileges: feel free to update the section below if I missed something important and am slow in editing this question)
---------------------------------------------------------------------------------------------------
GUIDE
GUIDE is probably the first tool new users will encounter. It is very useful for quickly putting something together, but it is otherwise fairly limited. It requires maintaining (and distributing) both a .m and a .fig file. Note that the GUIDE environment will be removed in a future release. After GUIDE is removed, existing GUIDE apps will continue to run in Matlab but they will not be editable in GUIDE. If you're starting a new GUI, don't use GUIDE. If you're updating an existing GUIDE GUI, migrate it to AppDesigner. In R2021a the first step for this removal was taken: all templates except the blank template have been removed.
GUILT
Although I haven't had a detailed look myself, it seems a list like this is not complete without at least mentioning the GUI Layout Toolbox, which is available on the file exchange and offers a lot of customization options.
Programmatic GUIs
You can bypass GUIDE and use the normal figures and functions like uicontrol to build GUIs from code. This makes the design less visual, but more flexible for future additions.
App Designer
The official successor to GUIDE, AppDesigner is not based on functions, but works similar to a class. It uses uifigure and mostly uses graphical elements that are incompatible with 'normal' GUIs that are created with a figure (or .fig).
Dear Sir or Madam
I tried to solve the cody-problem namend in the title.
Could you pleas tell me how I should name the vektor/variable in which it should be presentet?
Thank you for helping me.
Yours faithfully
Jann Borlinghaus
Dear MATLAB community,
How can I help my close friend who's bad at math and programming learn MATLAB?
He's a final year chemical engineering student who struggles even to plot two functions on the same graph in his computational fluid dynamics class (there was no prereq for matlab skills).
In his first year, I saw him get dragged through the introductory engineering classes which was his first encounter with MATLAB. Students were taught a few rudimentary programming skills and then were expected to make a code for a 'simple' tic-tac-toe game. It took him hours of blank looks and tutoring to even understand the simplest of boolean operators. He was never able to write a working function without the supervision of a friend or tutor. Needless to say, he was permanently scarred by the experience and swore to avoid using it forever.
After 3 years of avoiding MATLAB, he realised how not knowing it hurt him during his final year project. He had to solve a system of pdes to model the performance of a reactor and practically speaking, MATLAB was the most suitable software at hand. He ended up having to get a friend to help him code the equations in while also having to oversimplify his model.
The weird thing is that: most students from his chemical engineering faculty were not expected or encouraged to use MATLAB, almost all of their prior assignments required no use of MATLAB except that infamous first year course, and most of his peers also avoided using MATLAB and resorted to Excel. It is my understanding that Excel cannot match MATLAB's efficiency and clarity when solving calculus problems so it was not uncommon to see extremely long Excel spreadsheets.
Anyway, my friend is, with the help of a friend's past year MATLAB codes, trying to finish up his computational fluid dynamics assignment that's due soon. He finishes university in 2 weeks time.
Even though he knows that not every engineer has to use MATLAB in the workplace, he somehow wishes he was able to learn MATLAB at his glacial pace. I find it such a pity that he was never able to keep up with the pace of learning that was expected which begs the question: are students who are too slow at learning programming better of in a different field of study?
If you've managed to read to the end of this, thank you so much. I just don't know how to help my friend and I'm hoping some of you might be able to suggest how I can help him be better at it. I believe he has potential but needs special help when it comes to MATLAB.
All helpful and constructive suggestions considered,
Thank You All
I wrote a Cody problem, but I want to prevent people from using tricks to get a false "best" solution.
For example, many people do something like the following:
regexp '' '(?@"CODE HERE)';
in order to get the size of their program down to something quite small. I want to prevent this. I have seen people using some weird tests to try to block this, but I don't know how they work and when I try to copy them they fail.

Hi there! This is kind of an unusual question, but here it goes. I am a big time Matlab enthusiast and I met some of your representatives at Formula Student Germany back in August. There was a booth were your product was showcased but most importantly there was Matlab merchandise such as stickers, rub-on-tattoos and pens with the mathworks logo being handed out. This merchandise is increadibly popular with me and my nerdy friends. But sadly I didnt bring much with me from the event. Is it possible to get ahold some of it? Is it for sale? Are you willing to sponsor some geeky engineering students?

Would it make sense that, in order to enhance coding experience with practice exercises, each section of the Matlab Academy courses reference specific CODY problems related to that section so the CODY problems can be used in parallel with the structure of the Matlab Academy courses?
I am new in MATLAB programming. I want to learn matlab . I want to know about is any matlab or simulink contest available. Please answer me. Thanks
I started with Cody today and I found the file calculateSize.m https://de.mathworks.com/matlabcentral/fileexchange/34754-calculate-size which should determine the size of my solution. Unfortunately I do not get it to run. Can someone explain this to me or maybe explain how exactly the size of the solution is calculated?
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.
Gregory
Gregory
Last activity il 13 Giu 2017

Matlab webread (or urlread) Cody

Something seems to either have changed with webread/urlread behavior with R2016a or the Cody site has changed its authentication after it's September 2016 upgrade. Now, when ever I make a call using either webread (with weboptions) urlread using "My Cody" url, I get the html that corresponds to an unauthenticated user.
Ex: https://www.mathworks.com/matlabcentral/cody/players/1261697-gregory/solved
I've tried passing credentials using weboption and also cached the credentials using the built in Matlab browser - neither helped in seeing the authenticated version of this page.
Any help in understanding where the problem/solution lies would be helpful. Easily reproduced by running...
URL = 'https://www.mathworks.com/matlabcentral/cody/players/1261697-gregory/solved';
[Contents Status] = urlread(URL);
Compare this to the source pulled down when authenticated with Chrome (for example, search for the work "two"). FYI: this has worked for a couple of years up until now...
Matt Tearle
Matt Tearle
Last activity il 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.
O45
O45
Last activity il 23 Ott 2018

Best solution to cody problems

Hi, I am uploading the answers to cody problems. Although most of answers are correct but my size is bigger than the best answer. How can I view the best answer?
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.