126 reputation
5
bio website ilorentz.org/beenakker
location Leiden, The Netherlands
age
visits member for 1 year, 4 months
seen 2 days ago
physicist at Leiden University

Sep
24
awarded  Autobiographer
Jul
13
comment Integer Solutions To Linear Equation
khanacademy.org/math/arithmetic/fractions/Equivalent_fractions/…
Jun
30
comment Represent an integer as a sum of n non-consecutive squares
hmm, does that answer the OP's question for any $n$?
Jun
8
comment Heat transfer: boundary conditions with fluid velocity
@mkl314 --- perhaps this discussion (on whether the $v\cdot n$ in the boundary condition should be multiplied by $u$ or by $u-u_b$) can be settled by just considering what would happen if you would open a window in your room; there's a draft ($v\cdot n\neq 0$), but the temperature inside and outside is the same ($u=u_b$). Surely one would not expect a temperature gradient to appear?
Apr
23
awarded  Teacher
Apr
22
answered How to get transition matrix of markov process?
Mar
17
comment problem computing block inverse of factorized matix
then $U_1 U_1^T=1$, but you need $U_1^T U_1 =1$, which it's not.
Mar
13
awarded  Commentator
Mar
12
comment Equality that should be a consequence of Plancherel formula
just use that the Fourier transform with respect to $x$ of $u(x+y)$ is $e^{iy\xi}\hat{u}(\xi)$ and then apply Plancherel as usual.
Mar
9
comment problem computing block inverse of factorized matix
ask yourself what are the dimensions of $S$, $U$, $U_1$ and $U_2$, and you'll see your decomposition is not possible
Mar
8
comment problem computing block inverse of factorized matix
if you decompose $U$ into blocks you need four blocks, $U=\{\{B_1,B_2\},\{B_3,B_4\}\}$; none of the four blocks $B_n$ is unitary.
Feb
15
comment Laplace operator and Fourier transform
this holds in any dimension, doesn't it?
Jan
26
comment Derivative of the norm of a second order tensor w.r.t. the tensor
...which paper?
Dec
22
comment Global convergence for Newton's method in one dimension
isn't this answered here? mathoverflow.net/questions/148894
Dec
3
awarded  Supporter
Nov
10
comment f(x+C)/f(x) = const identifies potentiation?
your "const" is not constant, it is $C$-dependent.
Sep
25
answered Show that ∇²(fg)=∇∙ (∇[fg] = f∇²g+g∇²f+2(∇f ∙ ∇g)
Sep
12
comment Integral with Dirac delta (me or wolfram mathematica?)
with an answer on mathoverflow (I think Mathematica does just fine)
Jul
23
awarded  Editor
Jul
23
comment Exact form of pdf of maximum of normal random variables
for the delta function see: en.wikipedia.org/wiki/Dirac_delta_function --- and yes, the functions of $x$ and $y$ in the second line are to be integrated.