¬ just serendipity 🍀 (not just serendipity)

Alternative title: “Matlab, second impressions”. I am trying to learn Matlab super fast for prototyping purposes. Fast learning isn’t my preferred style for approaching a new programming language. However, this is necessary at the moment.

Disclaimer: This is not a tutorial. Just annotations and notes. Information is not necessarily correct, so consume it at your own risk.

Matlab Paradise #

• Everything is optimized for matrices and vectors. Matlab means “matrix laboratory”.
• A number is treated as a 1x1 matrix. This is really interesting and has nice implications and syntactic sugar.
• Matrix manipulation: A = [1,2,3] is a row vector; B = [1;2;3] is a column vector; C = [1,2;3,4] mixes them together.
• Slicing: Python style, but with different syntax. 1:10 means range(1,10) and 1:2:5 means range(1,5,2) but Matlab is inclusive (5 is present).
• Indexing vectors: A(1,2), A(2,1). Beware: indexes begin from 1, not zero.
• Performance: slow, slow, slow. See benchmarks on Julia’s homepage.
• matlab -nodesktop for command-line prompt. Self-contained, and you can still browse help with doc lu or help lu.
• Introspection #1: whos. Know everything about your variables.
• Workspace view: Really nice. Save variables with save out.mat. Load them with load out.mat.
• Some Unix goodness is available: ls, cd, pwd, ls -l.
• However, mkdir and rmdir work differently.
• Hello, world!: fprintf('string here') or display('hello, world!').
• Strings are enclosed with single quotes, not double. Why?
• Functions: C/C++/Java style. f(a,b,c,d,e).
• Some functions have more than one return value: ret1, ret2 = f(a,b,c).
• Clear screen: C-l or clc.
• Beware! clear deletes your variables. clear var is more specific. clear all is even more destructive.
• Auto-completion with TAB. No C-Space.
• Need help? lu( then F1. Hints? C-F1.
• Matlab hotkeys seem optimized for emacs users. See C-y (yank/paste), C-k (kill/copy), C-a and C-e (navigation), C-s (search), C-_ (undo).
• open file.m to open files without the fancy GUI.
• delete file.m. Not rm.
• Comments with percent sign (%). Why not hashes?
• Run a Matlab script: cd into its directory then type file<CR> in the prompt.
• version! R2014a == 8.3.0.x
• C-c for long computations.
• rand(2,2) if you ran out of creativity for numbers.
• v = [1 2] equals v = [1,2]. Who needs commas?
• Element-wise operators are preceded with a dot. Example: .*.
• Love intelligent prompts: C-p, M-p, C-n, M-n, <UP>, <DOWN>.
• Miss your shell? system('echo Hello world!').
• File handling: fid = fopen('file.txt','w'); fprintf(fid,'...'); fclose(fid);

Introspection #

• which lu.m, which lu
• edit lu.m, edit lu
• help <command> spits output
• doc <command> opens help browser
• whos shows your variables and symbols and functions
• type <command>. Like Unix’s cat.
• Try double-clicking on a variable in your workspace
• path

Internals: Functions, variables, types, control flow #

• sum(a), min(a), max(a), median(a), var(a), prod(a), mean(a), size(a), mode(a), std(a)
• false is 0. true is 1. Case sensitive!
• isvector(a), isempty(a)
• Not is a tilde ~, not ! (C-style)
• Matrix indexing: Column 2: a(:,2); Line 2: a(2,:).
• inv(a) for inverse
• find (a < 3) filter
• 2^3 == 8
• Quick matrix generation: zeros, ones, eye, magic, rand
• Math: cos(pi), sin(pi), tan(pi), tanh(pi)
• More math: rad2deg(pi) == 180, deg2rad
• det(m), rank(m), trace(m), a,b = lu(m)
• if, elseif, else, end. No parenthesis required.
• for k=1:10; display('hey'); end
• while
• switch b; case 1; display('one'); end. No colon after cases.

Symbolic math library/toolbox #

• syms x y z shorthand for x = sym('x')
• x = sym('x', [2 1]) for a symbolic column vector
• f = x + y^2 symbolic function
• subs(f, [x y], [1 2]) evaluates the function
• gradient(f), hessian(f), ccode(f) magic functions!

Fancy stuff #

• diary on, diary off, help diary to record terminal sessions