1. Debugging M-Files Steve Gu Feb 08, 2008

2. Outline What’s Debugging? Types of Errors Finding Errors Debugging Example Using Debugging Features

3. What’s Debugging? Debugging is the process by which you can – Recognize a bug exists – Isolate source of bug – Identify cause of bug – Determine fix for bug

4. Types of Errors Syntax Errors – Misspelling – Omitting parenthesis – MATLAB detects most syntax error and display error message in the command window Run-time Errors – Modify the wrong variables – Perform a calculation incorrectly – Apparent when an M-file produces unexpected result

5. Find Errors For syntax errors – Easy – MATLAB’s error messages For Run-time errors – More difficult – Some useful techniques: Remove ; Add keyboard statements  K>>  type return Run M-file as a script Use the ‘depfun’: e.g,list = depfun('binomial','-toponly'); Use the MATLAB Editor/Debugger or debugging functions

6. Debugging Example –Binomial.m

7. Using Debugging Features Preparing for Debugging Setting Breakpoints Running an M-File with Breakpoints Stepping through an M-File Examining Values Correcting Problems and Ending Debugging

8. Preparing for Debugging Open the file – To use the Editor/Debugger Save changes

9. Setting Breakpoint Setting Breakpoints Using the Editor – Set/Clear Breakpoint Function Equivalent – dbstop in binomial at 14 – Some Useful related functions dbtype :Lists the M-file code dbstatus :Lists breakpoints

10. Running an M-File with Breakpoints Run M-file from command window or Editor K>> -------MATLAB is in debug mode The program is paused at the first breakpoint The function displayed in the Stack changes to reflect the current function

11. Stepping Through an M-File

12. Examining Values Viewing Datatips in the Editor/Debugger Viewing Values in the Array Editor

13. Viewing Values in Array Editor

14. Ending Debugging Quit Debugging Clear all the breakpoints in the file Make changes to the M-file Save M-file