918 reputation
419
bio website doc.ic.ac.uk/~strasdat
location London, United Kingdom
age 34
visits member for 2 years, 11 months
seen 2 days ago

PhD student in Robot Vision


Jul
2
awarded  Curious
Jun
7
answered Any name for a special matrix with only non-zero entry
May
29
comment Jacobian of exponential mapping in SO3/SE3
I think you are right, and the equation $\partial \frac{e_i(\omega)}{\partial \omega_k} = \exp(\omega)\cdot G_k$ is wrong. But why do you think: $e_i(\omega)=\exp(\omega)$ The comment you mentioned states $\partial \frac{\exp(\omega)}{\partial \omega_k} = \exp(\omega)\cdot G_k$, but not $\partial \frac{\exp(a_i\log(\exp(\omega)T))P_i-P_i^*}{\partial \omega_k} = \exp(\omega)\cdot G_k$.
Apr
11
awarded  Revival
Dec
31
comment Optimization Problem - a rod inside a hallway
Sorry, this is no help. But this problem is somehow related to the hard "moving sofa" problem, so I thought I provide a link: math.stackexchange.com/questions/533436/…
Dec
9
revised Can axis/angle notation match all possible orientations of a rotation matrix?
edited body
Nov
29
revised Curves with “constant speed”?
clarification
Oct
25
comment How do “proofs” work in mathematics, down to the basic level?
@Cuc $1+2+4+6+8$ can be a statement depending on the definition of the symbols. Sorry, I could not resist!
Oct
23
answered Getting started with Lie Groups
Oct
20
revised Curves with “constant speed”?
edited tags
Oct
19
comment Quaternions as group of rotation and scaling
Well yes, scaling and rotations commutes. And if we analyzed rotation, the direct product of rotation and scaling is trivial. But on the other hand, complex numbers are often discussed using polar coordinates (rotation and scaling), and here we don't usually focus on unit complex numbers only.
Oct
19
revised Curves with “constant speed”?
deleted 3 characters in body; edited title
Oct
18
revised Curves with “constant speed”?
edited title
Oct
18
asked Curves with “constant speed”?
Oct
1
comment Speeding up the convergence for Steepest Descent Method
In general, the gradient does not point in the right direction, e.g. if you look at cs.cmu.edu/~quake-papers/painless-conjugate-gradient.pdf, Fig. 17. Actually, in this particular case, I guess a factor smaller one would help, more like Ritalin than espresso.
Sep
30
comment Confusion related to derivative of a vector
Well wikipedia says the Jacobian is written as $\frac{\partial (F_1, ..., F_m)}{\partial (x_1,...,x_n)}$ and this is just the special case for the constant function with $F=\theta$ and $x=\theta$. To be very precise, we probably have to transpose one of the two $\theta$'s...
Sep
30
revised Confusion related to derivative of a vector
added 219 characters in body
Sep
30
answered Confusion related to derivative of a vector
Sep
28
comment How can I determine a transformation matrix between two 3D datasets?
google.com/search?q=Least-squares+fitting+of+two+3-d+point+sets
Sep
28
comment General question about matrix calculus with specific example (with attempted answer)
The main question is: What does the derivative of $||Ax||$ with respect to $A$ mean? Isn't it just the collection of all partial derivatives ($\frac{\partial ||Ax||}{\partial A_{i,j}}$ for all $i,j$)?