795 reputation
512
bio website
location Chemnitz, Germany
age 27
visits member for 3 years, 7 months
seen Dec 8 at 20:43

Dec
8
awarded  Caucus
Sep
16
awarded  Notable Question
May
15
awarded  Yearling
Apr
6
awarded  Popular Question
Mar
2
comment How many squares actually ARE in this picture? Is this a trick question with no right answer?
Of course, what else. I wonder how this couldn't be a definite answer, a square is a square.
May
15
awarded  Yearling
Feb
27
accepted Dihedral angles between tetrahedron faces from triangles' angles at the tip
Feb
27
comment Dihedral angles between tetrahedron faces from triangles' angles at the tip
Since you were the first one to come up with a solution, it hurts not giving you the credit of acceptance. But I have to make a decision and achille's answer is more elaborate. But +1, of course.
Feb
26
comment Dihedral angles between tetrahedron faces from triangles' angles at the tip
+1 Man, of course, the normal vectors with some vector arithmetics, nothing 'bout spherical trigonometry, me stupid!
Feb
26
comment Dihedral angles between tetrahedron faces from triangles' angles at the tip
@SSumner Thanks for this link. "But I have no idea how it works" - Well, it has the formulas written on the site (though I'm also not able to directly derive this from spherical trigonometry, but at least I got a formula). Maybe somebody comes up with a nice answer showing the actual derivation of those formulas.
Feb
26
revised Dihedral angles between tetrahedron faces from triangles' angles at the tip
added 2 characters in body
Feb
26
comment Dihedral angles between tetrahedron faces from triangles' angles at the tip
@SSummer Really? In the end the only thing I'm uncertain of is the bottom plane of the supposed tetrahedron and this plane's location shouldn't change the dihedral angles between the other three faces. The tip's angles should completely define the tip triangles' locations relative to each other, shouldn't it? If I'm wrong on this, you could make the counter-proof an answer.
Feb
26
asked Dihedral angles between tetrahedron faces from triangles' angles at the tip
Jun
8
awarded  Caucus
May
15
awarded  Yearling
Apr
24
comment What is the formula of the following?
I don't currently get what you mean by "the three orthogonal tangent planes". In each point of the ellipsoid you have one unique tangent plane. Or do you mean all triplets of pairwise orthogonal planes that are tangent to the ellipsoid? And of course I second the above three comments.
Apr
11
comment Intersection between 3D closed contour and 3D plane
@msotaquira A line-plane intersection is an extremely trivial operation. Come back when your contour has thousands of points to talk about computational expense.
Apr
10
comment Intersection between 3D closed contour and 3D plane
@msotaquira Well, then it's not a contour, is it? So you're rather asking for a good way to define a contour using those points, which is entirely dependent on the context and your needs. But using a simple piecewise linear curve, as Mark suggests in his answer (and AakashM assumed in his comment) would be a good start.
Mar
13
comment I have to show that the matrix $M^TM$ is SPD if and only if the columns of the matrix M are linearly independent
@t.b. I have never seen it anywhere before, but Ok, according to your link it seems apprpriate.
Mar
13
revised I have to show that the matrix $M^TM$ is SPD if and only if the columns of the matrix M are linearly independent
fixed formatting and error in last equation