Portage’s current excuse for refusing to complete an emerge -pv world is that something wants choldmod with +supernodal, but it cannot find that. (That any little thing should completely block a --pretend is absurd, but that is a different bug.) The Changelog says: 03 Jan 2013; Sébastien Fabbro <bicatali@gentoo.org> cholmod-2.0.1.ebuild: Use generic pkg-config, replace supernodal with easier lapack use flag but sci-libs/suitesparse depends on: >=sci-libs/cholmod-2.0.1[cuda?,doc?,metis?,supernodal?] and is now broken by that change.
+ 08 Jan 2013; Sébastien Fabbro <bicatali@gentoo.org> suitesparse-4.0.2.ebuild: + Changed flag from supernodal to lapack to match cholmod, bug #450726 +