## Learn to Use ITensor

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# Running Your Program in Debug Mode

Compiling a code based on ITensor which is in "debug" mode is easy if you use the Makefile provided in the itensor/tutorial/project_template/ folder.

One you set up this Makefile correctly, by editing the fields at the top then you can compile your program in optimized mode by just typing make and in debug mode by typing make debug.

The command make debug creates an executable whose name is the usual name of your program (what you set the APP variable to in the Makefile) but with an extra -g appended at the end. So if APP=myappname then doing make debug will produce an executable called myappname-g.

A program compiled in debug mode differs from an optimized program in a few key ways:

• A debug-mode program contains many extra checks within ITensor which make sure you are using ITensor in the correct ways. For example, the .real method used to obtain ITensor components will perform bounds checking.

• Debug mode does not optimize your code, so that all of the original functions and function names are still used (otherwise the optimizer could inline some functions into others).

• Debug mode inserts various debugging symbols which allow you to use a program such as gdb (on Linux) or lldb (on Mac) to monitor the execution of your program and examine the call stack whenever you pause the program or when an error occurs.

When you suspect your program contains a bug, often it is helpful to run your program in debug mode to see if ITensor reports a more helpful error message. Some checking is disabled in fully optimized ITensor programs for maximum speed.

If ITensor still doesn't report a helpful enough error message, you can run your debug-mode program in a C++ debugger to get a more fine-grained report of what state your program was in when it crashed.

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