3,037 reputation
1247
bio website regularize.wordpress.com
location Braunschweig, Germany
age 36
visits member for 4 years
seen 4 hours ago

Professor at TU Braunschweig.

Area: Inverse problems, regularization theory, applied functional analysis, mathematical image processing.


Sep
12
comment How does the distribution of Erdős number evolve over time ? How to build a model to fit the real data ?
I suspect that the assumption that the Nummer of new articles and mathematicians is constant is false and guess that both grow superlinearly if not exponentially (at least for the next few years - eventually it may be logistical growth...).
Sep
11
comment Checking the intersection of two sets
Of course, you could also use @EmilJeřábek's formulation and use the constraints $l\leq Xy\leq u$.
Sep
11
answered Checking the intersection of two sets
Sep
11
comment Checking the intersection of two sets
This is a convex feasibility problem and could be solved, e.g. by alternating projections.
Sep
8
comment “Paradoxes” in $\mathbb{R}^n$
The unit ball is indeed a special convex body.
Aug
14
comment Heuristic interpretation of the 'third index' for Besov and Triebel-Lizorkin spaces
That's all well but I don't get a heuristic interpretation of $q$ out of it. Sure, the embeddings are clear but in what sense is $q$ some "fine tuning"? Probably the case $q=\infty$ is interesting: Although the spaces $B^s_{p,\infty}$ are not Sobolev spaces one somehow sees a link to Sobolev regularity. Do you know an example of a function in $B^s_{p,\infty}$ that does not lie in $B^s_{p,p}$? Maybe for $p=2$?
Aug
14
revised Heuristic interpretation of the 'third index' for Besov and Triebel-Lizorkin spaces
only fixed umlauts
Aug
13
reviewed Reject suggested edit on Matching number and chromatic number
Aug
1
comment Finding gradient of an optimization
You optimize over a binary variable (which seems to be a binary matrix, right?)? And you want the gradient of the objective with respect to this binary variable $w$? Better relax to $w_{ij}\in[0,1]$ or so. Also: What do you mean by "but for $T(t_i,w)$ is changing in each time step"?
Jul
30
comment Spectral multipliers vis-a-vis Differential geometry
Sorry but I don't really get the last motivating questions. Do you say that you would be satisfied by an answer like "Somebody else uses this stuff for something."? But probably this is just my ignorance for the works you point to.
Jul
26
awarded  Nice Answer
Jul
25
comment Intuition for Integral Transforms
See also the first chapter of "A guide to distribution theory and Fourier transforms" by Strichartz.
Jul
25
comment Decomposition of an integral operator into a composition
I heard that the chebfun2 package for MATLAB can perform some kind of LU decomposition for functions defined on the unit square…
Jul
25
comment Intuition for Integral Transforms
(cont) and this is "testing against a characteristic function". Well, that does not fit perfectly to test functions since these are $C^\infty$ but well - the physical world tends to be a bit fuzzy anyway…
Jul
25
comment Intuition for Integral Transforms
@TomCopeland I thought that "testing against a function" has a meaning in a physical sense. Consider the quantity you would like to test as some physical quantity, e.g. the temperature distribution in your office or the sugar concentration in your cup of tea. What should you do if you would like to know the value of this at a certain point? [In mathematical terms: do point evaluation.] As a physicist you realize that can't do perform this kind of "test". But what you can do, is to evaluate some kind of "average" (e.g. by taking out some sample of tea with a pipette) (to be continued)
Jul
24
revised Both NP-hard but different
corrected spelling, expanded tsp
Jul
24
comment Proximal operator of modified L1 matrix norm
There are simple rules for the prox of translations (just do substitution in the minimization problem). For the last case I only expect a simple solution for invertable $M$ (again substitute).
Jul
24
answered Examples of famous 'workhorse' theorems
Jul
21
comment Is this graph of reciprocal power means always convex?
Ok, my believe is destroyed… Another interesting question could be. What are $n$ and $p$ such that the respective function has most negative value in its second derivative?
Jul
21
comment Is this graph of reciprocal power means always convex?
Good! It still puzzles me, why the quantity is convex in almost every case. I would still believe if somebody told me that convexity is true for large $n$…