Matter AI | Code Reviewer Documentation

MATLAB Anti-Patterns Overview

Growing Arrays in Loops

% Anti-pattern: Growing arrays in loops
result = [];
for i = 1:1000
    result(i) = i^2;
end

% Better approach: Pre-allocate arrays
result = zeros(1, 1000);
for i = 1:1000
    result(i) = i^2;
end

% Even better: Use vectorization
i = 1:1000;
result = i.^2;

Avoid growing arrays incrementally in loops. MATLAB needs to reallocate memory and copy the entire array each time it grows, which is very inefficient. Instead, pre-allocate arrays to their final size before filling them, or use vectorized operations to avoid loops entirely.

Using Loops Instead of Vectorization

% Anti-pattern: Using loops for element-wise operations
A = rand(1000, 1000);
B = rand(1000, 1000);
C = zeros(1000, 1000);

for i = 1:1000
    for j = 1:1000
        C(i,j) = A(i,j) + B(i,j);
    end
end

% Better approach: Use vectorized operations
A = rand(1000, 1000);
B = rand(1000, 1000);
C = A + B;

Avoid using loops for element-wise operations on arrays. MATLAB is optimized for vectorized operations, which are much faster and more concise. Use MATLAB’s built-in vectorized functions and operators whenever possible.

Using eval and str2func

% Anti-pattern: Using eval
for i = 1:10
    varname = ['var' num2str(i)];
    eval([varname ' = ' num2str(i^2) ';']);
end

% Anti-pattern: Using str2func with dynamic function names
func_name = 'sin';
f = str2func(func_name);
y = f(x);

% Better approach: Use arrays or cell arrays
var = zeros(1, 10);
for i = 1:10
    var(i) = i^2;
end

% Better approach: Use function handles directly or from a container
func_map = containers.Map({'sin', 'cos', 'tan'}, {@sin, @cos, @tan});
func_name = 'sin';
if isKey(func_map, func_name)
    f = func_map(func_name);
    y = f(x);
end

Avoid using eval and str2func with dynamically constructed strings. These functions can execute arbitrary code, making your program vulnerable to code injection if the strings come from external sources. They also make code harder to debug and maintain. Use arrays, cell arrays, or containers.Map to store multiple values or function handles instead.

Using Global Variables

% Anti-pattern: Using global variables
global data config;

function processData()
    global data;
    % Process data
end

function saveResults()
    global data config;
    % Save results using data and config
end

% Better approach: Pass variables as parameters
function data = processData(data)
    % Process data
end

function saveResults(data, config)
    % Save results using data and config
end

% Usage
data = loadData();
config = loadConfig();
data = processData(data);
saveResults(data, config);

Avoid using global variables. They create hidden dependencies between functions, make code harder to understand and test, and can lead to unexpected behavior. Instead, pass variables explicitly as function parameters and return values.

Not Using Functions for Code Organization

% Anti-pattern: Long scripts without functions
% Script.m
% Load data
data = load('data.mat');

% Process data
% ... many lines of processing code ...

% Plot results
% ... many lines of plotting code ...

% Save results
% ... many lines of saving code ...

% Better approach: Organize code into functions
% Main script
function main()
    data = loadData('data.mat');
    processedData = processData(data);
    plotResults(processedData);
    saveResults(processedData, 'results.mat');
end

function data = loadData(filename)
    data = load(filename);
end

function processedData = processData(data)
    % Process data
    processedData = ...
end

function plotResults(data)
    % Plot results
end

function saveResults(data, filename)
    % Save results
    save(filename, 'data');
end

Avoid writing long scripts without breaking them into functions. This makes code harder to understand, test, and reuse. Instead, organize your code into functions with clear responsibilities, and use a main script or function to coordinate their execution.

Using clear all/close all/clc

% Anti-pattern: Using clear all/close all/clc in scripts
clear all;
close all;
clc;

% Load and process data
% ...

% Better approach: Be specific about what to clear
% Only clear variables you need to clear
clear x y z;

% Only close figures you need to close
close(figHandle);

Avoid using clear all, close all, and clc in scripts and functions, especially those that might be called by other scripts or functions. These commands affect the entire MATLAB environment, not just your script’s scope, which can lead to unexpected behavior and make debugging more difficult. Instead, be specific about what variables to clear and what figures to close.

Not Handling Errors Properly

% Anti-pattern: Not handling errors
fileID = fopen('data.txt', 'r');
data = fscanf(fileID, '%f');
fclose(fileID);
% If file doesn't exist, this will crash without a helpful message

% Better approach: Use try-catch for error handling
try
    fileID = fopen('data.txt', 'r');
    if fileID == -1
        error('Could not open file data.txt');
    end
    data = fscanf(fileID, '%f');
    fclose(fileID);
catch ME
    disp(['Error: ' ME.message]);
    % Handle the error appropriately
    if exist('fileID', 'var') && fileID ~= -1
        fclose(fileID);
    end
end

Always handle errors properly in your code. Use try-catch blocks to catch and handle exceptions, check return values from functions that might fail, and provide meaningful error messages. This makes your code more robust and easier to debug.

Using i and j as Variable Names

% Anti-pattern: Using i and j as variable names
for i = 1:10
    for j = 1:10
        % Using i and j as loop indices
    end
end

% Later in the code
z = x + i*y;  % Oops! i might not be the imaginary unit anymore

% Better approach: Use different variable names for indices
for ii = 1:10
    for jj = 1:10
        % Using ii and jj as loop indices
    end
end

% Now i and j still refer to the imaginary unit
z = x + 1i*y;  % Even better: use 1i instead of i

Avoid using i and j as variable names, especially for loop indices. In MATLAB, i and j are predefined as the imaginary unit (√-1), and overwriting them can lead to unexpected behavior in complex arithmetic. Use ii, jj, or other names for loop indices, and consider using 1i instead of i for the imaginary unit.

Using Magic Numbers

% Anti-pattern: Using magic numbers
% Calculate area of a circle
area = 3.14159 * radius^2;

% Convert temperature from Celsius to Fahrenheit
tempF = tempC * 1.8 + 32;

% Better approach: Define constants
PI = 3.14159;  % Even better: use pi
area = PI * radius^2;

% Better: use pi
area = pi * radius^2;

% Define conversion factors
C_TO_F_SCALE = 1.8;
C_TO_F_OFFSET = 32;
tempF = tempC * C_TO_F_SCALE + C_TO_F_OFFSET;

Avoid using magic numbers (hardcoded numeric literals) in your code. Instead, define constants with meaningful names at the beginning of your script or function. This makes your code more readable, maintainable, and less prone to errors. For mathematical constants like π, use MATLAB’s built-in constants (e.g., pi).

Ignoring Code Vectorization Opportunities

% Anti-pattern: Missing vectorization opportunities
result = zeros(length(x), 1);
for i = 1:length(x)
    if x(i) > 0
        result(i) = sqrt(x(i));
    else
        result(i) = 0;
    end
end

% Better approach: Use logical indexing and vectorization
result = zeros(size(x));
positive = x > 0;
result(positive) = sqrt(x(positive));

Don’t miss opportunities for vectorization. MATLAB provides many ways to avoid loops, such as logical indexing, vectorized functions, and array operations. Look for patterns in your code where you’re performing the same operation on many elements, and try to vectorize them.

Not Using Logical Indexing

% Anti-pattern: Using loops for filtering
data = rand(1000, 1);
filtered = zeros(1000, 1);
count = 0;

for i = 1:length(data)
    if data(i) > 0.5
        count = count + 1;
        filtered(count) = data(i);
    end
end

filtered = filtered(1:count);

% Better approach: Use logical indexing
data = rand(1000, 1);
filtered = data(data > 0.5);

Use logical indexing to filter arrays instead of loops. Logical indexing is a powerful MATLAB feature that allows you to select elements based on conditions. It’s much faster and more concise than using loops.

Inefficient File I/O

% Anti-pattern: Reading a file line by line
fileID = fopen('data.txt', 'r');
data = {};
i = 1;

while ~feof(fileID)
    line = fgetl(fileID);
    data{i} = line;
    i = i + 1;
end

fclose(fileID);

% Better approach: Read the entire file at once
fileID = fopen('data.txt', 'r');
data = textscan(fileID, '%s', 'Delimiter', '\n');
fclose(fileID);
data = data{1};

% Or even simpler
data = readlines('data.txt');  % In newer MATLAB versions

Avoid inefficient file I/O operations, such as reading a file line by line in a loop. Instead, use functions like textscan, readtable, readmatrix, or readlines (in newer versions) to read the entire file at once. These functions are optimized for performance and make your code more concise.

Not Using Built-in Functions

% Anti-pattern: Reimplementing built-in functionality
% Calculate mean manually
sum_val = 0;
for i = 1:length(data)
    sum_val = sum_val + data(i);
end
mean_val = sum_val / length(data);

% Find maximum value manually
max_val = data(1);
for i = 2:length(data)
    if data(i) > max_val
        max_val = data(i);
    end
end

% Better approach: Use built-in functions
mean_val = mean(data);
max_val = max(data);

Don’t reinvent the wheel by implementing functionality that already exists in MATLAB. MATLAB provides a vast library of built-in functions that are optimized for performance. Familiarize yourself with common functions for statistics, linear algebra, signal processing, and other domains relevant to your work.

Using Nested Loops for Matrix Operations

% Anti-pattern: Using nested loops for matrix operations
A = rand(100, 100);
B = rand(100, 100);
C = zeros(100, 100);

for i = 1:100
    for j = 1:100
        for k = 1:100
            C(i,j) = C(i,j) + A(i,k) * B(k,j);
        end
    end
end

% Better approach: Use built-in matrix operations
A = rand(100, 100);
B = rand(100, 100);
C = A * B;

Avoid using nested loops for matrix operations like multiplication, transposition, or inversion. MATLAB’s built-in matrix operations are highly optimized and much faster. Use operators like *, ', and functions like inv instead of implementing these operations manually.

Not Using Appropriate Data Structures

% Anti-pattern: Using arrays for heterogeneous data
names = {'Alice', 'Bob', 'Charlie'};
ages = [25, 30, 35];
scores = [95, 85, 90];

% Accessing data for a specific person is cumbersome
person_idx = find(strcmp(names, 'Bob'));
bob_age = ages(person_idx);
bob_score = scores(person_idx);

% Better approach: Use structures or tables
% Option 1: Structure array
people(1).name = 'Alice';
people(1).age = 25;
people(1).score = 95;

people(2).name = 'Bob';
people(2).age = 30;
people(2).score = 85;

people(3).name = 'Charlie';
people(3).age = 35;
people(3).score = 90;

% Accessing data for a specific person
bob_idx = find(strcmp({people.name}, 'Bob'));
bob = people(bob_idx);

% Option 2: Table (in newer MATLAB versions)
people = table(names', ages', scores', 'VariableNames', {'Name', 'Age', 'Score'});

% Accessing data for a specific person
bob = people(strcmp(people.Name, 'Bob'), :);

Use appropriate data structures for your data. For heterogeneous data with named fields, use structures or tables instead of parallel arrays. For large, homogeneous numerical data, use arrays. For sparse matrices, use sparse arrays. Choosing the right data structure can make your code more readable and efficient.

Not Using Cell Arrays Appropriately

% Anti-pattern: Using cell arrays inappropriately
% Storing numeric data in cell arrays
data = {1, 2, 3, 4, 5};
sum_val = 0;
for i = 1:length(data)
    sum_val = sum_val + data{i};
end

% Better approach: Use numeric arrays for numeric data
data = [1, 2, 3, 4, 5];
sum_val = sum(data);

% Anti-pattern: Not using cell arrays when appropriate
% Storing strings of different lengths
names = ['Alice   '; 'Bob     '; 'Charlie '];

% Better approach: Use cell arrays for strings
names = {'Alice', 'Bob', 'Charlie'};

Use cell arrays appropriately. Cell arrays are useful for storing heterogeneous data or data of varying sizes, like strings of different lengths. However, they’re less efficient than regular arrays for homogeneous numeric data. Use regular arrays for numeric data and cell arrays for mixed data types or varying-size data.

Not Using Function Handles

% Anti-pattern: Not using function handles
% Implementing numerical integration manually
function result = integrate(func_name, a, b, n)
    dx = (b - a) / n;
    result = 0;
    for i = 1:n
        x = a + (i - 0.5) * dx;
        if strcmp(func_name, 'sin')
            result = result + sin(x) * dx;
        elseif strcmp(func_name, 'cos')
            result = result + cos(x) * dx;
        elseif strcmp(func_name, 'exp')
            result = result + exp(x) * dx;
        else
            error('Unknown function');
        end
    end
end

% Better approach: Use function handles
function result = integrate(func, a, b, n)
    dx = (b - a) / n;
    result = 0;
    for i = 1:n
        x = a + (i - 0.5) * dx;
        result = result + func(x) * dx;
    end
end

% Usage
area1 = integrate(@sin, 0, pi, 1000);
area2 = integrate(@cos, 0, pi, 1000);
area3 = integrate(@exp, 0, 1, 1000);

% Even better: Use built-in integration functions
area1 = integral(@sin, 0, pi);

Use function handles to pass functions as arguments to other functions. This is more flexible and efficient than passing function names as strings and using conditional statements. Function handles also enable you to use anonymous functions for simple operations.

Not Using Profiler for Performance Optimization

% Anti-pattern: Guessing where performance bottlenecks are
% Adding random optimizations without measuring

% Better approach: Use the MATLAB Profiler
% profile on;
% myFunction();  % Run the function you want to profile
% profile viewer;  % View the profiling results

Don’t guess where performance bottlenecks are in your code. Use the MATLAB Profiler to identify which parts of your code are taking the most time. The Profiler provides detailed information about execution time for each line and function call, helping you focus your optimization efforts where they’ll have the most impact.

Not Using Appropriate Comments and Documentation

% Anti-pattern: Insufficient or excessive comments
% Insufficient
function y = f(x)
    y = x.^2 + 2*x + 1;
end

% Excessive
function y = f(x)
    % Assign x squared to y
    y = x.^2;
    % Add 2 times x to y
    y = y + 2*x;
    % Add 1 to y
    y = y + 1;
end

% Better approach: Use appropriate comments and documentation
function y = f(x)
    % f - Compute the quadratic function y = x^2 + 2x + 1
    %
    % Syntax:  y = f(x)
    %
    % Inputs:
    %    x - Input value or array
    %
    % Outputs:
    %    y - Result of the quadratic function
    
    y = x.^2 + 2*x + 1;
end

Use appropriate comments and documentation in your code. Comments should explain why the code does something, not what it does (which should be clear from the code itself). Use MATLAB’s help comment format for functions to provide documentation that can be accessed with the help command.

Not Using Meaningful Variable Names

% Anti-pattern: Using cryptic variable names
function r = c(a, b)
    r = sqrt(a^2 + b^2);
end

% Better approach: Use meaningful variable names
function hypotenuse = calculateHypotenuse(sideA, sideB)
    hypotenuse = sqrt(sideA^2 + sideB^2);
end

Use meaningful variable and function names that clearly indicate their purpose. This makes your code more readable and easier to maintain. Avoid single-letter variable names except for very common conventions (like i and j for loop indices, but even then, be careful as mentioned earlier).

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