postgresql autoincrement in migration

Hi
   I have a migration to be created with id start from say 100 for
example.That is not from 1
So I tried like

create_table :problems, :options => "auto_increment = 100" do |t|
    t.column :title, :text

Hi
   I have a migration to be created with id start from say 100 for
example.That is not from 1
So I tried like

create_table :problems, :options => "auto_increment = 100" do |t|
    t.column :title, :text
     ------
end

     I am using postgres .But the above auto_increment is mysql syntax i
think(Am I right?).And is not working also.How can I change that to get
the result?Please help

Hi
    Thanks for the reply
Sijo