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Below are some FAQs for the Cody contest 2020. If you have any additional questions, ask your questions by replying to this post. We will keep updating the FAQs.
Q1: If I rate a problem I solved before the contest, will I still get a raffle ticket?
A: Yes. You can rate any problem you have solved, whether it was before or during the contest period.
Q2: When will I receive the contest badges that I've earned?
A: All badges will be awarded after the contest ends.
Q3: How do I know if I’m the raffle winner?
A: If you are a winner, we will contact you to get your name and mailing address. You can find the list of winners on the Cody contest page .
Q4: When will I receive my T-shirt or hat?
A: You will typically receive your prize within a few weeks. It might take longer for international shipping.
Q5: I'm new to Cody. If I have some questions about using Cody, how can I get help?
A: You can ask your question by replying this post. Other community users might help you and we will also monitor the threads. You might also find answers here .
Q6: What do I do if I have a question about a specific problem?
A: If the problem description is unclear, the test suite is broken, or similar concerns arise, post your question(s) as a comment on the specific problem page. If you are having a hard time solving a problem, you can post a comment to your solution attempt (after submitting it). However, do not ask other people to solve problems for you.
Q7: If I find a bug or notice someone is cheating/spamming during the contest, how can I report it?
A: Use Web Site Feedback . Select "MATLAB Central" from the category list.
Q8: Why can't I rate a problem?
A: To rate a problem, you must solve that problem first and have at least 50 total points.
It's pretty odd how a solution that uses more characters than usual can be the "leading solution" of a Cody problem and have the least size. Compare these two codes that find the sum of integers from 1 to 2^x, which one uses fewer characters, thus should be the better solution?
function y = sum_int(x)
regexp '' '(?@y=sum(1:2^x);)'
end
function ans = sum_int(x)
sum(1:2^x)
end
Meta threads have a tendency to grow large. This has happened several times before (the wishlist threads #1 #2 #3 #4 #5, and 'What frustrates you about MATLAB?' #1 and #2).
No wonder that a thread from early 2011 has also kept growing. After just under a decade there are (at time of writing) 119 answers, making the page slow to load and navigate (especially on mobile). So after a friendly nudge; here is a new thread for the things that are missing from Matlab.
Same question: are there things you think should be possible in Matlab, but aren't? What things are possible with software packages similar to Matlab that Matlab would benefit from? (note that you can also submit an enhancement request through support, although I suspect they will be monitoring activity on this thread as well)
What should you post where?
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)
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
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).
This is the 5th installment of the wish-list and bug report thread.
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). The third started out as New design of the forum - grey on white and the fourth MATLAB Answers Wish-list #4 (and bug reports) is also growing so large it is slow to load and navigate.
Same idea as the previous ones: one wish (or bug report) per answer, so that people can vote their wishes.
What should you post where?
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)
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
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.
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 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:
- Slow
- Buggy
- Security Risk
- Difficult to Work With
- Obfuscated Code Intent
- Confuses Data with Code
- Code Helper Tools do not Work
- Magically Making Variables Appear in a Workspace is Risky
There are much better alternatives to accessing dynamic variable names:
- Indexing into Cell Array or ND-Array
- Non-scalar Structures (with Indexing)
- Dynamic Field-Names in a Structure
- load into a Structure, not into the Workspace
- save the Fields of a Scalar Structure
- Use a table or timetable Array
- Use more Efficient Ways to Pass Variables Between Workspaces
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.
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.
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...
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.
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?
What should you post where?
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)
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.
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.
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