Paul Breiding, Khazhgali Kozhasov, Antonio Lerario
Abstract We investigate some geometric properties of the real algebraic variety
$$\Delta $$ Δ of symmetric matrices with repeated eigenvalues. We explicitly
compute the volume of its intersection with the sphere and prove a
Eckart–Young–Mirsky-type theorem for the distance function from a generic matrix
to points in $$\Delta $$ Δ . We exhibit connections of our study to real
algebraic geometry (co... hiện toàn bộ
Picard–Vessiot theorem (1910) provides a necessary and sufficient condition for
solvability of linear differential equations of order n by quadratures in terms
of its Galois group. It is based on the differential Galois theory and is rather
involved. Liouville in 1839 found an elementary criterium for such solvability
for $$n=2$$ . Ritt simplified Liouville’s theorem (1948). In 1973 Rosenlicht
pro... hiện toàn bộ