all but homepage as singlecol (blix)

I’m using blix for a new site, and the header has the following code which makes some pages “singlecol” and other pages double (allowing for the sidebar). Since I am only using the sidebar on the home (index.php) page, I want everything else to be “singlecol.” Does anyone know how I can modify this code correctly? I made a few stabs at it myself, but I either got error messages, or nothing happened… (I’m not very good at this!)

<div id="container"<?php if (is_page() && !is_page("archives")) echo " class=\"singlecol\""; ?>>