Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help copyfields”.

  COPYFIELDS copies a selection of the fields from one structure to another
 
  Use as
    b = copyfields(a, b, fields);
  which copies the specified fields over from structure a to structure b. Fields that
  are specified but not present will be silently ignored.
 
  See also KEEPFIELDS, REMOVEFIELDS, RENAMEFIELDS