fatal error: arpack.h: No such file or directory

This error message indicates that the compiler is unable to locate the header file "arpack.h". This header file is typically used in programs that use the ARPACK library for solving large-scale eigenvalue problems.

To resolve this issue, you need to ensure that the ARPACK library is properly installed on your system and that the necessary header files are included in the compiler's search path.

Here are some steps you can take to troubleshoot this error:

1. Check that the ARPACK library is installed on your system. You can do this by searching for the library files (e.g. libarpack.so) in your system's library directories (e.g. /usr/lib).

2. If the library is not installed, you can download it from the ARPACK website (http://www.caam.rice.edu/software/ARPACK/) and install it on your system.

3. If the library is installed, check that the header file "arpack.h" is included in the library's installation directory. This file should typically be located in a directory named "include" within the library's installation directory.

4. If the header file is not in the library's installation directory, check that it is installed on your system. You can do this by searching for the file using your system's file search utility.

5. Once you have located the header file, you need to add its directory to the compiler's search path. This can be done by adding the directory to the INCLUDE environment variable or by adding the directory to the compiler's command line options using the -I flag.

By following these steps, you should be able to resolve the "arpack.h: No such file or directory" error and successfully compile your program.