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Nov 21, 2015 at 16:51 comment added Ali Taghavi what is the structure of the Lie algebra of this Lie group?
Nov 21, 2015 at 16:03 vote accept Ali Taghavi
Nov 21, 2015 at 16:02 comment added Mostafa - Free Palestine @Ali Yes, indeed the closed sets are exactly the orbits of matrices with an upper bound on rank. For the second question, I think $(\mathbb C^*)^n$ action on toric varieties provide a large set of examples.
Nov 21, 2015 at 15:58 comment added Ali Taghavi Are there some other natural examples that a lie group act on a compact connected manifold but the quotien is a finite non Haussdorfn space?
Nov 21, 2015 at 15:51 comment added Ali Taghavi because the rank is upper semi continuous?
Nov 21, 2015 at 15:50 comment added Mostafa - Free Palestine @AliTaghavi Yes, I think it's only determined by rank and so the quotient is a finite set of size $min(m,n)+1$ but its topology is not discrete.
Nov 21, 2015 at 15:43 comment added Ali Taghavi Thank you for your answer. Does the orbits determined ONLY by rank? If so, is the quotion space a finite discrete space? Is not this strange?
Nov 21, 2015 at 15:32 history answered Mostafa - Free Palestine CC BY-SA 3.0