MATLAB

## Indexing - 1-based indexing — first element is `A(1)`, not `A(0)` - `end` keyword for last index — `A(end)`, `A(end-1)`, works in any dimension - Linear indexing on matrices — `A(5)` accesses 5th element column-major order - Logical indexing returns vector — `A(A > 0)` gives 1D result regardless of A's shape ## Matrix vs Element-wise - `*` is matrix multiplication — `.*` for element-wise - `/` solves `A*x = B` — `./` for element-wise division - `^` is matrix power — `.^` for element-wise power - Forgetting the dot is silent bug — dimensions might accidentally match ## Vector Shape Matters - Row vector: `[1 2 3]` or `[1, 2, 3]` — shape is 1×3 - Column vector: `[1; 2; 3]` — shape is 3×1 - Transpose with `'` (conjugate) or `.'` (non-conjugate) — for complex, they differ - `*` between row and column gives scalar or matrix — depending on order ## Array Preallocation - Growing arrays in loops is slow — preallocate: `A = zeros(1000, 1)` - `zeros`, `ones`, `nan` for preallocation — specify size upfront - Cell arrays: `cell(n, m)` — preallocate cells too ## Broadcasting - Implicit expansion since R2016b — `A + b` works if dimensions compatible - Singleton dimensions expand — `[1;2;3] + [10 20]` gives 3×2 - Before R2016b needed `bsxfun` — legacy code may still use it ## NaN Handling - `NaN ~= NaN` is true — use `isnan()` to check - Most operations propagate NaN — `sum([1 NaN 3])` is NaN - Use `'omitnan'` flag — `sum(A, 'omitnan')`, `mean(A, 'omitnan')` ## Cell Arrays vs Matrices - `{}` for cell arrays — hold mixed types, different sizes - `()` indexing returns cell — `C(1)` is 1×1 cell - `{}` indexing extracts content — `C{1}` is the actual value - Comma-separated list from `C{:}` — useful for function arguments ## Common Mistakes - `=` for assignment, `==` for comparison — `if x = 5` is error in MATLAB - Semicolon suppresses output — forget it and flood command window - `clear` removes all variables — use `clearvars` for selective, `close all` for figures - `i` and `j` are imaginary unit — don't use as loop variables, or reassign explicitly - String vs char: `"text"` vs `'text'` — double quotes are string arrays (R2017a+) ## Functions - Anonymous functions: `f = @(x) x^2` — quick inline functions - Multiple outputs: `[a, b] = func()` — must capture or use `~` to ignore - `nargin`/`nargout` for optional args — check how many inputs/outputs provided - `varargin`/`varargout` for variable args — cell array of extra arguments ## Debugging - `dbstop if error` — breakpoint on any error - `keyboard` in code pauses execution — enter debug mode at that line - `whos` shows variable sizes — `size(A)` for specific variable