Debugging in MATLAB

MATLAB Tutorial

🐞 Debugging in MATLAB

Debugging in MATLAB is the process of finding, understanding, and fixing errors in code using built-in tools like breakpoints, step execution, workspace inspection, and error messages.

It is essential for writing correct, efficient, and reliable programs.
MATLAB is developed by MathWorks.

🔹 Why Debugging Is Important

  • Identifies logical and runtime errors

  • Helps understand program flow

  • Saves development time

  • Improves code quality

1️⃣ Common Types of Errors

Type Example
Syntax Error Missing end
Runtime Error Index out of bounds
Logical Error Wrong output but no error

2️⃣ Using Breakpoints (Most Important Tool)

🔸 Set Breakpoint (Editor)

  • Click the dash (—) next to line number

  • Turns into a red dot

📌 Execution pauses at breakpoint.

🔸 Example Code


When run, MATLAB stops at the breakpoint so you can inspect variables.

3️⃣ Step Execution Commands

When paused at a breakpoint:

Command Action
Step Execute current line
Step In Enter function
Step Out Exit function
Continue Run to next breakpoint

📌 Available in Editor toolbar.

4️⃣ Command-Line Debugging (dbstop, dbstep)

🔸 Stop on Error

dbstop if error

📌 MATLAB pauses exactly where the error occurs.

 Step Line by Line

dbstep

 Continue Execution

dbcont

 Clear Debug Mode

dbclear all

5️⃣ Inspecting Variables

While paused:

  • Workspace window shows current values

  • Hover mouse over variables

  • Use Command Window to evaluate expressions

r
a

6️⃣ Using disp() and fprintf() for Debugging

Quick way to trace logic.


📌 Useful when breakpoints aren’t convenient.

7️⃣ Debugging Logical Errors

Example:


✔ Correct:


📌 Debug by checking intermediate results.

8️⃣ Using keyboard Command

Pauses execution and enters interactive debug mode.


9️⃣ Error Stack & Messages

When an error occurs:

  • MATLAB shows error message

  • Click the file name to jump to error line

  • Use Call Stack window to trace function calls

🔟 Best Debugging Practices

  • Debug small blocks of code

  • Use meaningful variable names

  • Validate inputs early

  • Remove unused variables

  • Combine breakpoints with print statements

🎯 Interview Questions: Debugging in MATLAB

🔹 Q1. What is debugging?

Answer:
Finding and fixing errors in code.

🔹 Q2. How do you stop execution when an error occurs?

Answer:
dbstop if error.

🔹 Q3. What is a breakpoint?

Answer:
A marker where execution pauses for inspection.

🔹 Q4. How do you step through code line by line?

Answer:
Using Step / dbstep.

🔹 Q5. What does keyboard do?

Answer:
Pauses execution and enters debug mode.

🔹 Q6. How do you debug logical errors?

Answer:
By inspecting variable values and program flow.

✅ Summary

  • MATLAB provides strong debugging tools

  • Breakpoints are the most powerful feature

  • Command-line tools enable advanced control

  • Essential skill for exams & real projects

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