I understand that you are not able to find documentation about the "LibGetRecordWidth" function.
The "LibGetRecordWidth" function returns the width of the specified record as an integer. This function is one of the 'Miscellaneous Functions' in the TLC Library. Refer to the following link for more details:
Definition of this function can be accessed by typing the following command in the MATLAB Command Window:
>> edit([matlabroot '/rtw/c/tlc/lib/dtypelib.tlc']);
For other functions in the TLC Library, refer to the following link: