This function reads and parses platform annotation table (*.annot) for NCBI Gene Expression Omnibus(GEO). Platform annotation table contain information about platforms.

Input:
filename: filename of the *.annot file
Output:
annotation: platform annotation info platform_table: platform table

Example:
1) obtain a *.annot file
e.g. from ftp://ftp.ncbi.nlm.nih.gov/geo/platforms/GPL2nnn/GPL2883/annot/GPL2883.annot.gz
unzip the file, you will get: GPL2883.annot
2) put the function and the annot file in your working directry, or addpath
3) run function
[annotation, platform_table]=read_annot_file('GPL2883.annot');