Do they really? See e.g. this http://crookedtimber.org/2012/05/30/in-soviet-union-optimization-problem-solves-you/ http://crookedtimber.org/2012/05/30/in-sovie

Do they really? See e.g. this http://crookedtimber.org/2012/05/30/in-soviet-union-optimization-problem-solves-you/ http://crookedtimber.org/2012/05/30/in-soviet-union-optimiza... which is a discussion of the difficulties of computerized central planning and argues that -- even allowing for approximate solutions being good enough, and even allowing for computers to get much faster -- we don't have algorithms that would allow for real-time central planning of a real economy, and even if we did there would be substantial further problems in actually doing it. (It's in the context of Francis Spufford's book "Red Plenty" -- which is actually pretty much about computerized central planning, I believe -- and it's by Cosma Shalizi who is a very smart guy, knows a lot about economics, and is sufficiently leftist to be more than averagely sympathetic to the idea of a planned economy.)