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May
21
answered Find the ratio of curved surface area of frustum to the cone.
Apr
22
comment How can the centers of these 5 related circles be specified as a formula?
Try the email given at the bottom of this page.
Apr
22
awarded  Revival
Mar
24
answered Name of specific symmetric Toeplitz matrix
Mar
20
comment Point inside the area of two overlapped triangles
There is nothing simple about this question, since there are a number of ways two triangles can overlap. The overlapping region may include none of the 6 vertices of the two triangles, so you really do need to resort to a very generic triangle-triangle intersection routine, then pick some arbitrary point in the intersecting region.
Mar
19
comment Silly Error calculating eigenvalues of a 3x3?
Did you typo the last row of your matrix swapping $a$ and $b$?. For me, Mathematica gives the expected hand obtained results.
Mar
19
answered Eigenvalue of the sum of a symmetric matrix and the outer product of it's eigenvector
Mar
19
comment Understanding the QR eigenvalue finding algorithm
@Ron Thompson: I believe so.
Mar
19
answered Understanding the QR eigenvalue finding algorithm
Mar
19
comment Understanding the QR eigenvalue finding algorithm
Apologies if this is what you're doing, but I'm not sure I understand what you're saying. If the subdiagonal element $h_{j+1,j}$ has converged to zero, then the next shift should be $h_{j,j}$. Also, I stand corrected... the code does not help :) Java is so verbose...
Mar
19
comment Understanding the QR eigenvalue finding algorithm
Can you post your test matrix and the $H$ in the iteration before it is zeroed? Also, the code would be helpful. Are you always choosing the last element of the main diagonal, or are you choosing the diagonal element above the unconverged part?
Mar
19
comment pseudo inverse of symmetric matrix product?
@Jerry Guern: Apparently I meant "generalized reflexive inverse". You are right that the pseudoinverse is unique. The problem is that $S^{-1}M^\dagger S^{-1}SMS$ is not necessarily Hermitian since $S^{-1}M^\dagger M S^{-1}$ is not necessarily hermitian (even though $M^\dagger M$ is).
Mar
18
comment pseudo inverse of symmetric matrix product?
The pseudo-inverse is not unique. Both forms in Mathematica give a valid pseudoinverse.
Mar
18
answered How to quickly determine the inverse of elementary matrices?
Mar
18
answered Why do I get a big relative error for my function? (Numerical Analisys - floating point)
Mar
14
comment Using Principal Directions and Curvatures to Find Point On Surface
You only have information about the surface in the neighborhood of a $n$, so you can't be sure how the surface behaves at any finite distance away from $n$. You can assume that the surface is smooth with constant principal curvatures (so that $n$ is at the apex of a perfect ellipsoid), then the locus of points a given distance from $n$ is a sphere and you can intersect the sphere with the ellipsoid.
Mar
13
answered How can the centers of these 5 related circles be specified as a formula?
Mar
13
answered Eigenvectors of almost-Toeplitz tridiagonal matrix.
Mar
12
answered Area of a square inscribed in a circle
Mar
12
comment psuedo inverse of a matrix counter-example
In that case, then the second part of my answer with the counterexample still works.