could not find function "principal"

The error message "could not find function 'principal'" typically indicates that R is unable to locate the 'principal' function, which may be due to a number of reasons, such as misspelling the function name, not loading the required package or library, or not defining the function in the script. To fix this issue, you can try the following steps:

1. Check if you have spelled the function name correctly.
2. Load the package or library that contains the 'principal' function using the 'library' or 'require' function.
3. Check if you have defined the 'principal' function in your script, or if you have defined it in another script, make sure to source that script before calling the function.
4. If none of the above solutions work, try reinstalling the package or library that contains the 'principal' function.