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visits member for 2 years, 6 months
seen Sep 22 at 11:53

Sep
18
accepted Prove that a matrix is positive definite and symmetrical
Sep
18
comment Prove that a matrix is positive definite and symmetrical
Thank you. I will try to work something out. One thing that is certain is that $X^TX$ is symmetric, because $(X^TX)^T = X^T(X^T)^T = X^TX$. By the Spectral theorem, it follows that $X^TX$ can be decomposed into matrices of eigenvectors and eigenvalues. Now I should be able to show $v^TX^TXv \geq 0$ for all vectors v I think. And thank you Karl (below) for providing the hint of transpose of $X^TX$
Sep
17
asked Prove that a matrix is positive definite and symmetrical
Jul
2
awarded  Curious
May
7
comment Prove that the two integrals are equal with periodic function
Perfect, thank you. I need to work more with technical arguments like this rather than conceptual ones.
May
7
accepted Prove that the two integrals are equal with periodic function
May
6
asked Prove that the two integrals are equal with periodic function
May
3
awarded  Yearling
May
3
comment Evaluate limits by interpreting sums as integral sums
Thank you, very good answer.
May
3
accepted Evaluate limits by interpreting sums as integral sums
May
2
comment Evaluate limits by interpreting sums as integral sums
What does it mean to interpret sums as integral sums.
May
2
asked Evaluate limits by interpreting sums as integral sums
Apr
7
asked Prove that THEOREMS is NP-complete
Apr
5
comment Wrong way to use MVT to prove inequality
Thank you all, I guess it is a good idea to REALLY understand the meaning of the MVT. I rushed to fast into doing problems.
Apr
5
accepted Wrong way to use MVT to prove inequality
Apr
4
asked Wrong way to use MVT to prove inequality
Apr
4
asked Differentiable and unbounded function problem
Apr
3
accepted Prove uniform convergence using the M-test
Apr
1
asked Prove uniform convergence using the M-test
Mar
21
comment Radius of convergence problem
Thank you sir! Cauchy-Hadamard formula on the sum from $n=0$ would give $\frac{1}{R}$ right?