다음에 대한 결과:
Explore resources, ask questions, and discuss topics related to using Simulink to apply power electronics control to Electric Vehicles, Renewable Energy, Battery Systems, Power Conversion, and Motor Control. This is the 3rd MATLAB Central community, after Maker and SimBiology , and is moderated by Tony Lennon . Tony is the Power Electronics Marketing Manager at MathWorks.
Visit the community here . As always, let us know what you think by liking this post or commenting below.
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)
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?
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.
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.
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!
We all know that MATLAB is probably the best software for engineering purposes, I think it's a little expensive unless you have it for free on your school or place you work, please share your opinion about MATLAB cost, including toolboxes, student versions... is it that expensive?
This topic is for unexpected or bizarre or humorous references to MATLAB. Specific citations would be appreciated.
I love MATLAB. It is so quick and easy to write software to do what you want. It has excellent debugging and profiling tools. It is cross platform, making code easy to share (assuming the other people have forked out for the not-so-cheap license). It has interfaces to other software.
However, there are some things about it that irk me. I'd like to hear from other people what things annoy them about MATLAB.
---------------------------------
Because this thread has become so large it is slow to load and navigate. Please post new answers in the second thread.
---------------------------------
What is the best way to learn MATLAB at home without a tutor?
As asked by Vieniava in "How to make a list of user's reputation?", some of us came up with interesting ideas on how to fill an updated list with the reputation scores of the contributors to Answers.
I took the initiative to compile a public list of users with meta info:
- position (desc ordering by reputation)
- id
- nickname (truncated to fit the page)
- reputation
- # of comments
- # of questions asked
- % accept rate
- # of posts answered
- # of accepted answers
The code used to compile the list is available at the bottom.
EDIT
TMW team implemented a page with the metascores: http://www.mathworks.com/matlabcentral/answers/contributors
Please refer to it and congrats to the team!
Use this function to retrieve info from the link above:
function [metainfo, elapsedTime] = metainfo(type,order)
% METAINFO - Retrieve metainfo on contributors to www.matworks.com/.../answers
%
% METAINFO Retrieve data sorted by reputation in descending order
%
% METAINFO(TYPE,ORDER) Specify TYPE and sorting ORDER as
% type : 'reputation'
% 'questions'
% 'answered'
% 'accepted'
%
% order: 'asc'
% 'desc'
%
% Examples:
%
% % Standard call (rep, disc)
% info = metainfo;
%
% % Sort by question answered in descending order
% info = metainfo('an','d');
%
% See also: URLREAD, REGEXP
% Author: Oleg Komarov (oleg.komarov@hotmail.it)
% Tested on R14SP3 (7.1) and on R2009b. In-between compatibility is assumed.
% 28 feb 2011 - Created
tic
% Check # inputs
error(nargchk(0,2,nargin))
% Retrieve inputs
if nargin == 0
type = 'reputation';
order = 'desc';
end
if ~exist(type,'var')
sortTypes = {'reputation','questions','answered','accepted'};
type = sortTypes{strncmp(type,sortTypes,numel(type))};
order = 'desc';
end
if ~exist(order,'var')
orderTypes = {'asc','desc'};
type = orderTypes{strncmp(order,orderTypes,numel(order))};
end
% Build url string
url = ['http://www.mathworks.com/matlabcentral/answers/contributors?'...
'dir=' order '&sort=' type '&page='];
% First read
[page, ok] = urlread([url '1']);
% Catch number of pages to read
if ok
totcon = regexp(page,'>1 - 50 of (\d+)','tokens');
totcon = dataread('string',totcon{1}{1},'%d');
nPages = ceil(totcon/50);
else
error('Cannot read ".../contributors?page=1"')
end
% Loop over contributors pages
metainfo = cell(totcon,7);
metainfo(1:end,1) = num2cell(1:size(metainfo,1));
for p = 1:nPages
if ok
endpos = 50*p;
% Id, Rep
expr = '><a href="\/matlabcentral\/answers\/contributors\/(\d+)';
data = regexp(page, expr,'tokens');
if 50*p > totcon; endpos = 50*(p-1)+numel(data); end
metainfo(1+(p-1)*50:endpos,2) = [data{:}];
% Nickname
expr = ['"Reputation: (\d+)">([\w\ ' reshape([repmat(92,1,137);33:59,61:64,91:97,123:126,161:255],1,[]) ']+)</a></h2>'];
data = regexp(page, expr,'tokens');
metainfo(1+(p-1)*50:endpos,[4,3]) = cat(1,data{:});
% Qcount, Ans, Acc
data = regexp(page, '<span >(\d+)</span>[A-z<>"-\s\/]+','tokens');
metainfo(1+(p-1)*50:endpos,5:7) = reshape(cat(1,data{:}),3,[]).';
else
error('Metainfo import stopped. \nCannot read ".../contributors?page=%d"',p)
end
[page, ok] = urlread([url sprintf('%d',p+1)]);
end
% Convert to doubles
metainfo(:,[2,4:7]) = cellfun(@str2double,metainfo(:,[2,4:7]),'un',false);
elapsedTime = toc;
This topic (which was not started by Mathworks) is for features you would like to see for this MATLAB Answers facility.
I suggest one wish per answer, so that people can vote for individual 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)
