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13h
answered Show that we cannot have a prime triplet of the form $p$, $p + 2$, $p + 4$ for $p >3$
18h
comment I've tried to work out a calculation in my physics book, but the book is telling me one answer and my calculator is telling me another one.
Are you sure they're using $\sin$ as opposed to $\sin^{-1}$ (that is, arcsin)? As things stand, it seems strange that the answer should be in degrees.
18h
comment Receiving different answers
((-1.1)^6-1)/((-1.1)^3-1)
1d
comment Verify rotation relation between two matrices
"There should be an easier way": I don't think it gets easier that finding $AA^T$ and $BB^T$. Also, note that if you solve for $U$, then unless $A,B$ are tall matrices of full rank, you will have multiple solutions.
1d
revised Determinant of this matrix?
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1d
comment Find only the real eigenvalues of a matrix.
Note that the characteristic polynomial is a real-valued functions whose zeros you can search for using numerical methods. Note however, that this requires you calculate a determinant every time you want one value of the function.
1d
comment What does $-p \ln p$ mean if p is probability?
@Ruslan $-\ln p_i$ is the information gained if the $i$th event occurs, and $\sum p_i(-\ln p_i)$ is the expected amount of information gained
1d
comment What does $-p \ln p$ mean if p is probability?
Do you know what "expected value" means?
1d
comment Finding a matrix inverse when an equation involving it is a multiple of the identity matrix
@egreg there's also the fact that yours was 15 seconds earlier
1d
comment Finding the Determinant of a particular Matrix
One nice approach is to note that this matrix is a rank-1 update of a relatively nice matrix (the one with only $x$s on the diagonal).
1d
comment Finding the Determinant of a particular Matrix
Should the last diagonal entry be an $x^2$?
1d
answered Finding a matrix inverse when an equation involving it is a multiple of the identity matrix
1d
answered Is it true that for all matrices $A$ and all traceless matrices $T$, there exists a traceless matrix $T'$ such that $AT = T'A$?
1d
answered Understanding Defiinition of Vector Space
1d
revised Minimizing the error by finding optimum step-size
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1d
comment Minimizing the error by finding optimum step-size
Please consider changing the title to something that describes the statement you're proving
1d
revised Minimizing the error by finding optimum step-size
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1d
comment Perturbation theory for a symetric rank-one update
See the Sherman Morrison formula for the bit about inverses. I think that Bhatia's Matrix Analysis has all the inequalities for this kind of thing
1d
comment Perturbation theory for a symetric rank-one update
There are nice things you can say about the singular values, and there are theorems about "updating" the inverse
1d
comment Let A be a square matrix such that $A^3 = 2I$
If you know about minimal polynomials, it suffices to note that the minimal polynomial of $A$ divides $x^3 - 2$. So, $A - \lambda I$ will necessarily be invertible if $\lambda^3 \neq 2$.