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olivier dot begassat dot cours at gmail dot com


Jan
18
reviewed Approve 2 equations — please explain
Jan
18
reviewed Approve How many matrix colorings are possible?
Jan
18
reviewed Approve 2 equations — please explain
Jan
18
reviewed Approve $G$ is a finite group, Show that if $[G:Z(G)] = 21$ then exists $H ,K < G$ such that $H\neq G$ and $K \neq G$ and $HK = G$
Jan
18
comment Signature of quadratic form $Q(p)=p(1)p(2)+p(3)p(4)$
The matrix for $n=2$ is incorrect, I'll correct it later.
Jan
18
answered Signature of quadratic form $Q(p)=p(1)p(2)+p(3)p(4)$
Jan
18
reviewed Approve Determining if matrix is diagonalizable.
Jan
17
reviewed Approve Algorithm for bipartite graph
Jan
17
reviewed Reject Find the root of the polynomial?
Jan
17
reviewed Approve The definition of the exchange lemma
Jan
17
reviewed Approve Stressing out because I'm not sure how to complete the square
Jan
16
reviewed Approve Integrating two equations that equal, what happens to the constant on one of the sides?
Jan
16
answered Again, improper integrals involving $\ln(1+x^2)$
Jan
16
answered Approximated of $f:D \rightarrow \mathbb{C}$ by polynomials
Jan
16
comment Approximated of $f:D \rightarrow \mathbb{C}$ by polynomials
Is $D$ the open (or closed) unit disk? By polynomials, do you mean polynomials in one complex variable $P(z)=a_0+a_1 z+\cdots+a_nz^n$?
Jan
16
comment orientability of riemann surface
@GFR thanks! Yes: if $A$ is a complex matrix, there is a sequence $(A_n)$ of diagonalisable matrices converging to $A$. By continuity of the determinant, we have $$\det(A)=\lim_{n\to\infty}\det(A_n)$$ Actually, my argument is redundant if you know that every complex matrix is similar to an upper triangular matrix. This upper triangular matrix translates to an upper triangular real matrix of $2\times 2$ blocs, and the determinant of an upper triangular bloc matrix being the product of the determinants of the diagonal blocs gives the answer again. So no limits are required after all.
Jan
16
revised Existence of a sequence that converges to a polynomial
edited body
Jan
16
comment Existence of a sequence that converges to a polynomial
@Julien yes, typo on my part.
Jan
16
reviewed Leave Open Topology, continuous mapping help!!
Jan
16
reviewed Approve Fun logarithm question