You can't concatenate the numeric and string values in the argument list via [] nor the varying size of the first output line and the rest other than in a cell array and Matlab i/o functions aren't extended to handle cell arrays automagically. So it'd be simpler to write the code specific to the situation instead of trying to over-generalize. (Like the holy grail of vectorization, generalization is good, but sometimes can try to carry it beyond the realm of the practical).
First, since you want a header and have some text, decide on a field width. If the data are as shown simply a set of small integers, that's pretty simple; we'll just assume a one-character name as you've shown and a set of positive integers <100 so a field width of 3 will ensure at least one blank.
fid=fopen('yourfile');
% First just write the header since it's so simple as fixed string
fprintf(fid,' P F L S\n');
fmt=[repmat(1,3,'%3d') ' %s\n']); % format for first line included text
fprintf(fid,fmt,P(1),F(1),L,S) % write first row
fmt=repmat(1,2,'%3d') \n'); % format for remainder of file
fprintf(fid,fmt,[P(2:end).' F(2:end).'].') % NB: .' on array to output row order
fid=fclose(fid);
Since the two variables are vectors and you're writing a fixed number of columns, you don't need any count of the length. To write a general square 2D array you would count the number of columns and write the repmat statement argument to match; it's why I used the form here as demonstration even though writing a specifc number of repeated formats is easy enough here, in the general case it gets totally impractical. The idea is simple but until you've seen it, it isn't that obvious to build a dynamic format string this way. (Steven Lord of TMW showed me this "trick" years ago...it's just one of those things that comes along with Matlab since C from which the ML i/o is derived chose to not use a form for format control strings that allows for repeat field counts within the string a la Fortran FORMAT)
