I need open source software, or however a free software (i would download
and use it without pay!), for manage data with CART or Principal Component
Analysis. Tipically Matlab is the best software solution, but it isn't free!
GNU Octave is free but not more powerful! Then, please, could you help me?
Thanks by the poor poor little italian student Leo! :)

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You are asking in the wrong place. Try over on comp.ai.neural-nets or
sci.stat.math. I believe that, technically, the name "CART" is owned
by Salford Systems, so most commercial offerings will be called things
like "C&RT". Anyway, try the Software section at KDnuggets
(http://www.kdnuggets.com) for listings of free and commercial tools.
Will Dwinnell
http://will.dwinnell.com