Probably it goes something like this:
filename = 'OutputFileNameGoesHere.dat';
[fid, msg] = fopen(filename, 'w');
if fid < 0
error('failed to open file "%s" because "%s"', filename, msg);
end
IQDATA = [reshape(IDATA, 1, []); reshape(QDATA, 1, [])];
fwrite(fid, IQDATA, '*single');
fclose(fid)
... but perhaps it uses a different file format, or represents the IQ data as int16, or has headers...