MATLAB: What are the thought processes that go on when you are trying to solve a MATLAB problem

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I am (fairly) new to MATLAB, just started using it more heavily these past few months (before then I just used it to make basic plots). So when I have an issue I typically spend hours on just the (seemingly) simplest things such as how to remove certain values from structures and how to improve image quality for image analysis etc…

I just wanted to know if there is a particular thought process that you (everyone) go though before finding a solution to your exact problem. This might sound like a pretty dumb question but I think maybe learning about how other people tackle code related problems may be able to help me add good habits to what I do and make me improve.

Thanks

Best Answer

I make very heavy use of the debugger, in combination with the command line to try out syntax and options. I also often like to create quick scripts to test out alternative solutions to a problem where speed is an issue and I want to understand which is fastest.

I make heavy use of the offline documentation, using e.g.

doc ismember

or whatever function I want to use, looking at the 'See Also'; section or any other links from the page if the function itself is not what I want, but I feel I need something similar.

I keep a series of e-mails (effectively a blog, but for reasons not interesting here, e-mails were the chosen medium) in which I write up what I call 'Matlab Nuggets' which remind me (and my other team members, who I also send them to) about certain functions or how I solved a certain problem or reusable code I added to our repository. Basically just anything I think I or my team may find useful in future that i can search for.

Our team also has a fairly large repository of past code now so if I know I have solved a similar problem (or part of it) before I will do a search in our repository to find the relevant code if I can.

I also use other sources such as Matlab Answers and Yair Altman's Undoucmented Matlab blog, although this tends to be more hardcore! One of the main reasons I started answering questions on Matlab Answers is because it helps me learn. So many people post questions that can easily be answered just by testing out some syntax on command line - apparently they don't think of that, but me doing it and providing the answer they could just have easily found themselves helps various concepts or syntaxes sink into my brain too for future usage.

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MATLAB: “For improved robustness, consider replacing i and j by 1i” – Is this an error

Matlab uses i and j for imaginary i, or sqrt(-1). This lead to a lot of issues because i and j are often used as counter variables for the for and while loops. Example:

for i = 1:10
    plot(ano3, medial5(i-7), 'k');  %Did you mean imaginary i or counter variable i? 
end

In your case, it depends on if i is the imaginary i or a variable i. If imaginary i, take their advice and use 1i, or you may end up spending hours looking for the i bug. If variable i, you must declare i before hand, or it'll assume i = 1i.

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

I reject the label "expert", but here is my two cents worth anyway:

MATLAB Specific:

MATLAB has a great feature that very few programming languages have: readable documentation. Use it! Search it using your favorite internet search engine. Practice browsing it via the contents on the left-hand side (which are all hyperlinks). Understand how it is grouped by topic. Try out the examples. Use the help to locate related functions and advice on how to solve particular problems.
Read the help for every function and operation that you use, no matter how trivial you think that operation is. Half of the questions that we answer on this forum are solved by reading the documentation for the function/operator that the user is already using!
Learn to use the debugging tools. These are indispensable. Read about how they work and what they do, then practice using them! For starting debugging, the most useful command is: dbstop if error
Learn the differences between array and matrix operations, otherwise your calculations will simply produce nonsense and you won't know why. If you are not doing linear algebra you need array operations.
Learn about comma-separated lists, and the easy ways to use them.
Pay attention to all of the code warnings, error messages, underlining, and tips that the MATLAB Editor shows. Do not ignore these messages.
Make vectorized code your first choice when writing code, and leave those ugly low-level loops behind you... Understand why vectorized code is beautiful, and how it can be used to make your code much more efficient and easier to understand.
And of course when loops are required, always preallocate the arrays before the loops.
There are important ways to write fast and efficient code. Use them.
For example, use absolute or relative filepaths instead of slow and hard-to-debug cd.
Learn good MATLAB programing habits right from the start, because life is too short to un-learn bad habits! This means: comment your code, use consistent formatting, write help (with H1 line) in every function, pass variables properly, use input checking, never use eval (or assignin, feval, etc), etc.
Do not force meta-data (e.g. dates, times, indices, test parameters, etc) into variable names or fieldnames: meta-data is data, so store it as data in an array.
Use subs to substitute values into a symbolic expression and evaluate it. Do not use eval to do this, it is not the correct tool for the job!
Write functions, not scripts. Scripts are good for playing around with, but not for real work.
Refer to all graphics objects (figures, axes, lines, etc) using explicit handle references (e.g. using Parent property). This makes plotting and handling graphics robust and predictable. Do not assume that the current figure/axes/etc is going to be the one that your code needs to access.
Pass variables reliably using input/output arguments and do not use globals or assignin. If you need to pass lots of values (e.g. simulation parameters) then put them into a structure and pass that.
MATLAB blogs are an excellent source of inspiration and ideas. Loren Shure's blog is a mine of great ideas, and a veritable pleasure to read too.
Check out other people's code on File Exchange (FEX). Note that the comments are often more useful than the ratings... and you will soon get an idea of whose comments are particularly worth paying attention to.

General Advice:

Imagine that every script and function you write is going to be given to someone else... impress them!
Test everything thoroughly. Check each line as you write it. Does it really do what you think it is doing? Many beginners come here to ask for help because they only think about what they want their code to be doing, but never bother to actually check what their code really is doing. Code cannot read your mind.
Make a set of test-cases and collect all of the instances that fail while the code is being written, plus all the edge-cases and every case category that it needs to work with. You will not regret doing this.
Break problems into parts, solve the parts separately. Make functions for code that needs to be repeated: this allows code to be reused, and bug-fixed in one location. Scripts are great for quickly testing an idea, but functions are much more robust for anything that will be used for more than one day.
Think about what you are doing: actually think. What is the problem being solved? What is really the problem? How can it be solved? With what methods? Read Pólya's excellent book How To Solve It.
Don't get stuck believing that you have found the best solution... there can be a much better solution waiting just around the corner, that may just require a new perspective, a reformulation of the problem, or a slight rearrangement of the data.
Practice! Challenge yourself with tasks you want to solve, or take part in onlne code challenges or tutorials.

Best Answer

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