MATLAB

MATLAB Debugging

This chapter introduces Debugging in MATLAB, an essential skill for identifying and fixing errors in code. MATLAB provides robust tools and techniques to debug scripts and functions efficiently, enabling developers to ensure the correctness and reliability of their programs.

Chapter Goal

The goal of this chapter is to provide a comprehensive understanding of MATLAB’s debugging capabilities, focusing on:

  1. Learning how to use debugging tools such as breakpoints and the debugger interface.
  2. Understanding common debugging techniques and strategies.
  3. Exploring how to analyze and resolve errors effectively.
  4. Implementing best practices for efficient debugging workflows.

Key Characteristics for MATLAB Debugging

  1. Interactive Debugging: MATLAB’s debugger allows real-time inspection of variables and code execution.
  2. Breakpoint Management: Set, disable, and clear breakpoints to control program execution.
  3. Error Localization: Use error messages and stack traces to pinpoint issues.
  4. Call Stack Navigation: Inspect function call hierarchies to understand execution flow.
  5. Integration with Editor: Debugging tools are seamlessly integrated into MATLAB’s editor.

Basic Rules for MATLAB Debugging

  1. Set Breakpoints Strategically: Place breakpoints near suspected issues or critical operations.
  2. Inspect Variables: Check variable values during execution to detect anomalies.
  3. Step Through Code: Use Step, Step In, and Step Out to navigate through code line-by-line.
  4. Resolve Errors Sequentially: Address the first error in a sequence, as it may resolve subsequent issues.
  5. Use Diagnostic Tools: Leverage tools like dbstop, dbstep, and dbquit for advanced debugging.

Best Practices

  1. Reproduce Errors Consistently: Ensure errors can be consistently reproduced for effective debugging.
  2. Log Progress: Use diagnostic messages (disp, fprintf) to trace program execution.
  3. Minimize Code Changes: Avoid making significant changes while debugging to isolate issues effectively.
  4. Test Incrementally: Debug small code sections to identify issues early.
  5. Document Fixes: Record resolved issues and their solutions for future reference.

This chapter equips you with the skills to identify and resolve errors in MATLAB code efficiently, ensuring robust and reliable program development. Subsequent sections will delve into syntax, examples, and real-world applications.

Syntax Table

Serial No Component Syntax Example Description
1 Set Breakpoint dbstop in file at line Sets a breakpoint at the specified line in the file.
2 Remove Breakpoint dbclear in file at line Removes a breakpoint at the specified line in the file.
3 Display Call Stack dbstack Displays the function call stack at the current point of execution.
4 Pause Execution keyboard Pauses execution and enters debug mode for inspection.
5 Quit Debugging dbquit Exits debug mode and stops code execution.

Syntax Explanation

1. Set Breakpoint

What is Setting a Breakpoint?

A breakpoint pauses code execution at a specified line, allowing variable inspection and step-by-step execution.

Syntax:

dbstop in file at line;

Detailed Explanation:

  • Replace file with the filename and line with the line number where the breakpoint should be set.
  • Execution pauses when the breakpoint is encountered.

Example:

dbstop in myscript.m at 10;

run(‘myscript.m’);

Output:

Execution pauses at line 10 in myscript.m.

2. Remove Breakpoint

What is Removing a Breakpoint?

Removing a breakpoint resumes normal code execution without pauses at the specified line.

Syntax:

dbclear in file at line;

Detailed Explanation:

  • Specify the filename and line number of the breakpoint to remove.

Example:

dbclear in myscript.m at 10;

Output:

Breakpoint at line 10 in myscript.m is removed.

3. Display Call Stack

What is Displaying the Call Stack?

The call stack shows the sequence of function calls leading to the current execution point.

Syntax:

dbstack;

Detailed Explanation:

  • Displays a list of functions and their call order.
  • Useful for tracing the origin of an error or understanding execution flow.

Example:

dbstack;

Output:

Displays the call stack with function names and line numbers.

4. Pause Execution

What is Pausing Execution?

Pausing execution allows you to interactively inspect variables and modify code during runtime.

Syntax:

keyboard;

Detailed Explanation:

  • Inserts a pause in the code where the keyboard command is placed.
  • Execution resumes when you enter return.

Example:

x = 10;

keyboard; % Pause here

y = x + 5;

Output:

Execution pauses, allowing variable inspection and modification.

5. Quit Debugging

What is Quitting Debugging?

Exits debug mode and terminates the current code execution.

Syntax:

dbquit;

Detailed Explanation:

  • Use dbquit to exit debug mode and stop the program.
  • Ensures clean termination of debugging sessions.

Example:

dbquit;

Output:

Debugging session is terminated.

Notes

  • Use breakpoints strategically to avoid unnecessary pauses.
  • Combine dbstack with error handling to trace issues effectively.

Warnings

  • Avoid leaving keyboard or breakpoints in production code.
  • Overusing debugging commands can slow down development workflows.

Real-Life Project: Debugging a Financial Analysis Tool

Project Name: Identifying and Fixing Errors in a Financial Analysis Script

Project Goal:

To debug a MATLAB script that calculates compound interest for multiple investments, ensuring accurate results and robust error handling.

Steps in the Project:

  1. Set Up the Script:
    • Create a script to calculate compound interest for various inputs.
  2. Introduce Debugging Tools:
    • Add breakpoints and use diagnostic tools like disp to trace variable values.
  3. Identify Logical Errors:
    • Inspect the calculation logic for compound interest.
  4. Resolve Issues:
    • Fix syntax and logical errors identified during debugging.
  5. Verify Results:
    • Test the script with multiple datasets to ensure correctness.

Code for This Project:

% Step 1: Define the function for compound interest

function finalAmount = compoundInterest(principal, rate, time, n)

    try

        % Validate inputs

        assert(principal > 0, ‘Principal must be positive.’);

        assert(rate > 0 && rate <= 1, ‘Rate must be between 0 and 1.’);

        assert(time > 0, ‘Time must be positive.’);

        assert(n > 0, ‘Number of compounding periods must be positive.’);

 

        % Calculation

        finalAmount = principal * (1 + rate / n)^(n * time);

 

    catch ME

        disp([‘Error in compoundInterest: ‘, ME.message]);

        finalAmount = NaN; % Return NaN if error occurs

    end

end

 

% Step 2: Test the function with breakpoints

principal = 1000;

rate = 0.05;

time = 10;

n = 12;

 

% Insert breakpoint at the following line to inspect variables

finalAmount = compoundInterest(principal, rate, time, n);

 

disp([‘Final Amount: ‘, num2str(finalAmount)]);

Save and Run:

  1. Save the script as debug_financial_tool.m.
  2. Run the script in MATLAB.

Expected Output:

  1. Console Output:
    • Correct final amounts for valid inputs.
    • Descriptive error messages for invalid inputs.
  2. Debugging Insights:
    • Trace variables like principal, rate, and finalAmount to verify calculations.

Learning Outcomes:

  • Understand how to debug MATLAB scripts effectively.
  • Learn to identify and resolve logical errors in financial calculations.
  • Gain experience in using breakpoints and diagnostic tools for robust debugging.