You need to define your function with the input argument
function cac = cssm(fid)
then pass the function the file identifier, don't put it inside your function.
Why do you have code like this:
fid = urlwrite('http://www.ndbc.noaa.gov/data/realtime2/41115.spec','Rincon.txt'); % URL from CARICOOS
cac = cssm(fid)
and then on line two of your function, you have
fid = fopen('Rincon.txt');
??
Either declare the function with NO input arguments
function cac = cssm
and do everything internally, or pass, the function the fid argument and get the file identifier before you call the function.
