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references/octave-compatibility.md
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544
references/octave-compatibility.md
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# GNU Octave Compatibility Reference
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## Table of Contents
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1. [Overview](#overview)
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2. [Syntax Differences](#syntax-differences)
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3. [Operator Differences](#operator-differences)
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4. [Function Differences](#function-differences)
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5. [Features Unique to Octave](#features-unique-to-octave)
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6. [Features Missing in Octave](#features-missing-in-octave)
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7. [Writing Compatible Code](#writing-compatible-code)
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8. [Octave Packages](#octave-packages)
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## Overview
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GNU Octave is a free, open-source alternative to MATLAB with high compatibility. Most MATLAB scripts run in Octave with no or minimal modifications. However, there are some differences to be aware of.
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### Installation
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```bash
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# macOS (Homebrew)
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brew install octave
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# Ubuntu/Debian
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sudo apt install octave
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# Fedora
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sudo dnf install octave
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# Windows
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# Download installer from https://octave.org/download
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```
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### Running Octave
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```bash
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# Interactive mode
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octave
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# Run script
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octave script.m
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octave --eval "disp('Hello')"
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# GUI mode
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octave --gui
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# Command-line only (no graphics)
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octave --no-gui
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octave-cli
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```
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## Syntax Differences
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### Comments
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```matlab
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% MATLAB style (works in both)
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% This is a comment
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# Octave style (Octave only)
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# This is also a comment in Octave
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% For compatibility, always use %
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```
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### String Quotes
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```matlab
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% MATLAB: Single quotes only (char arrays)
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str = 'Hello'; % char array
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str = "Hello"; % string (R2017a+)
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% Octave: Both work, but different behavior
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str1 = 'Hello'; % char array, no escape sequences
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str2 = "Hello\n"; % Interprets \n as newline
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% For compatibility, use single quotes for char arrays
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% Avoid double quotes with escape sequences
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```
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### Line Continuation
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```matlab
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% MATLAB style (works in both)
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x = 1 + 2 + 3 + ...
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4 + 5;
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% Octave also accepts backslash
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x = 1 + 2 + 3 + \
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4 + 5;
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% For compatibility, use ...
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```
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### Block Terminators
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```matlab
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% MATLAB style (works in both)
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if condition
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% code
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end
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for i = 1:10
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% code
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end
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% Octave also accepts specific terminators
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if condition
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# code
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endif
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for i = 1:10
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# code
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endfor
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while condition
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# code
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endwhile
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% For compatibility, always use 'end'
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```
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### Function Definitions
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```matlab
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% MATLAB requires function in file with same name
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% Octave allows command-line function definitions
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% Octave command-line function
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function y = f(x)
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y = x^2;
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endfunction
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% For compatibility, define functions in .m files
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```
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## Operator Differences
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### Increment/Decrement Operators
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```matlab
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% Octave has C-style operators (MATLAB does not)
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x++; % x = x + 1
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x--; % x = x - 1
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++x; % Pre-increment
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--x; % Pre-decrement
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% For compatibility, use explicit assignment
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x = x + 1;
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x = x - 1;
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```
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### Compound Assignment
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```matlab
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% Octave supports (MATLAB does not)
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x += 5; % x = x + 5
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x -= 3; % x = x - 3
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x *= 2; % x = x * 2
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x /= 4; % x = x / 4
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x ^= 2; % x = x ^ 2
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% Element-wise versions
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x .+= y;
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x .-= y;
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x .*= y;
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x ./= y;
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x .^= y;
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% For compatibility, use explicit assignment
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x = x + 5;
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x = x .* y;
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```
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### Logical Operators
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```matlab
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% Both support
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& | ~ && ||
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% Short-circuit behavior difference:
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% MATLAB: & and | short-circuit in if/while conditions
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% Octave: Only && and || short-circuit
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% For predictable behavior, use:
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% && || for scalar short-circuit logic
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% & | for element-wise operations
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```
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### Indexing After Expression
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```matlab
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% Octave allows indexing immediately after expression
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result = sin(x)(1:10); % First 10 elements of sin(x)
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value = func(arg).field; % Access field of returned struct
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% MATLAB requires intermediate variable
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temp = sin(x);
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result = temp(1:10);
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temp = func(arg);
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value = temp.field;
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% For compatibility, use intermediate variables
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```
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## Function Differences
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### Built-in Functions
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Most basic functions are compatible. Some differences:
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```matlab
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% Function name differences
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% MATLAB Octave Alternative
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% ------ ------------------
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% inputname (not available)
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% inputParser (partial support)
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% validateattributes (partial support)
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% Behavior differences in edge cases
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% Check documentation for specific functions
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```
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### Random Number Generation
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```matlab
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% Both use Mersenne Twister by default
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% Seed setting is similar
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rng(42); % MATLAB
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rand('seed', 42); % Octave (also accepts rng syntax)
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% For compatibility
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rng(42); % Works in modern Octave
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```
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### Graphics
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```matlab
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% Basic plotting is compatible
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plot(x, y);
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xlabel('X'); ylabel('Y');
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title('Title');
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legend('Data');
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% Some advanced features differ
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% - Octave uses gnuplot or Qt graphics
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% - Some property names may differ
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% - Animation/GUI features vary
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% Test graphics code in both environments
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```
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### File I/O
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```matlab
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% Basic I/O is compatible
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save('file.mat', 'x', 'y');
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load('file.mat');
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dlmread('file.txt');
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dlmwrite('file.txt', data);
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% MAT-file versions
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save('file.mat', '-v7'); % Compatible format
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save('file.mat', '-v7.3'); % HDF5 format (partial Octave support)
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% For compatibility, use -v7 or -v6
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```
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## Features Unique to Octave
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### do-until Loop
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```matlab
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% Octave only
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do
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x = x + 1;
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until (x > 10)
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% Equivalent MATLAB/compatible code
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x = x + 1;
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while x <= 10
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x = x + 1;
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end
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```
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### unwind_protect
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```matlab
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% Octave only - guaranteed cleanup
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unwind_protect
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% code that might error
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result = risky_operation();
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unwind_protect_cleanup
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% always executed (like finally)
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cleanup();
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end_unwind_protect
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% MATLAB equivalent
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try
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result = risky_operation();
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catch
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end
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cleanup(); % Not guaranteed if error not caught
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```
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### Built-in Documentation
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```matlab
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% Octave supports Texinfo documentation in functions
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function y = myfunction(x)
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%% -*- texinfo -*-
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%% @deftypefn {Function File} {@var{y} =} myfunction (@var{x})
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%% Description of myfunction.
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%% @end deftypefn
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y = x.^2;
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endfunction
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```
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### Package System
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```matlab
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% Octave Forge packages
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pkg install -forge control
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pkg load control
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% List installed packages
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pkg list
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% For MATLAB compatibility, use equivalent toolboxes
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% or include package functionality directly
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```
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## Features Missing in Octave
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### Simulink
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```matlab
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% No Octave equivalent
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% Simulink models (.slx, .mdl) cannot run in Octave
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```
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### MATLAB Toolboxes
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```matlab
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% Many toolbox functions not available
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% Some have Octave Forge equivalents:
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% MATLAB Toolbox Octave Forge Package
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% --------------- --------------------
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% Control System control
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% Signal Processing signal
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% Image Processing image
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% Statistics statistics
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% Optimization optim
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% Check pkg list for available packages
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```
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### App Designer / GUIDE
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```matlab
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% MATLAB GUI tools not available in Octave
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% Octave has basic UI functions:
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uicontrol, uimenu, figure properties
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% For cross-platform GUIs, consider:
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% - Web-based interfaces
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% - Qt (via Octave's Qt graphics)
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```
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### Object-Oriented Programming
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```matlab
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% Octave has partial classdef support
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% Some features missing or behave differently:
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% - Handle class events
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% - Property validation
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% - Some access modifiers
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% For compatibility, use simpler OOP patterns
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% or struct-based approaches
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```
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### Live Scripts
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```matlab
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% .mlx files are MATLAB-only
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% Use regular .m scripts for compatibility
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```
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## Writing Compatible Code
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### Detection
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```matlab
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function tf = isOctave()
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tf = exist('OCTAVE_VERSION', 'builtin') ~= 0;
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end
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% Use for conditional code
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if isOctave()
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% Octave-specific code
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else
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% MATLAB-specific code
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end
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```
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### Best Practices
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```matlab
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% 1. Use % for comments, not #
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% Good
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% This is a comment
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% Avoid
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# This is a comment (Octave only)
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% 2. Use ... for line continuation
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% Good
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x = 1 + 2 + 3 + ...
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4 + 5;
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% Avoid
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x = 1 + 2 + 3 + \
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4 + 5;
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% 3. Use 'end' for all blocks
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% Good
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if condition
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code
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end
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% Avoid
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if condition
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code
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endif
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% 4. Avoid compound operators
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% Good
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x = x + 1;
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% Avoid
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x++;
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x += 1;
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% 5. Use single quotes for strings
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% Good
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str = 'Hello World';
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% Avoid (escape sequence issues)
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str = "Hello\nWorld";
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% 6. Use intermediate variables for indexing
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% Good
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temp = func(arg);
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result = temp(1:10);
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% Avoid (Octave only)
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result = func(arg)(1:10);
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% 7. Save MAT-files in compatible format
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save('data.mat', 'x', 'y', '-v7');
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```
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### Testing Compatibility
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```bash
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# Test in both environments
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matlab -nodisplay -nosplash -r "run('test_script.m'); exit;"
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octave --no-gui test_script.m
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# Create test script
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# test_script.m:
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# try
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# main_function();
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# disp('Test passed');
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# catch ME
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# disp(['Test failed: ' ME.message]);
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# end
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```
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## Octave Packages
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### Installing Packages
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```matlab
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% Install from Octave Forge
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pkg install -forge package_name
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% Install from file
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pkg install package_file.tar.gz
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% Install from URL
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pkg install 'http://example.com/package.tar.gz'
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% Uninstall
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pkg uninstall package_name
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```
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### Using Packages
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```matlab
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% Load package (required before use)
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pkg load control
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pkg load signal
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pkg load image
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% Load at startup (add to .octaverc)
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pkg load control
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% List loaded packages
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pkg list
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% Unload package
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pkg unload control
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```
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### Common Packages
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| Package | Description |
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|---------|-------------|
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| control | Control systems design |
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| signal | Signal processing |
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| image | Image processing |
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| statistics | Statistical functions |
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| optim | Optimization algorithms |
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| io | Input/output functions |
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| struct | Structure manipulation |
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| symbolic | Symbolic math (via SymPy) |
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| parallel | Parallel computing |
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| netcdf | NetCDF file support |
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### Package Management
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```matlab
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% Update all packages
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pkg update
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% Get package description
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pkg describe package_name
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% Check for updates
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pkg list % Compare with Octave Forge website
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```
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Reference in New Issue
Block a user