Didier Piau

4,193
Reputation
2471 views
Is this your account?

Registered User 

Name Didier Piau
Member for 3 years
Seen 11 hours ago
Website
Location
Age
May
15
comment Continuous Differentiability under Expectation
This is the classical problem of differentiation under the integral sign hence everything works fine under a domination condition. Not MO stuff.
May
10
accepted Probability that one RV will exceed many others
May
10
comment Markov transition probabilities and negative binomial distribution.
"A realization of a Markov process generates a sequence of interval lengths between transition from one state to another." These lengths are always exponentially distributed, hence to get other lengths distributions one must leave the realm of Markov processes. If this is what you have in mind, you might want to explain in more details.
May
10
comment Probability that one RV will exceed many others
You are welcome. Is this the way you like to proceed: to get a full answer, then to write an incomplete one yourself and to accept it?
May
10
comment Probability distribution for two-state system that depends on residence time
I find a tad surprising that an answer restricted to the symmetric case $\kappa_+=\kappa_-$ is "what you were looking for" since the modifications needed to solve the general case are non trivial. For this reason, to ask whether my answer and the accepted one are the same seems rather moot and I do not feel much motivation to answer your last query. But since you seem happy with what you got, everything is perfect. (Unrelated: one cannot accept two answers.)
May
8
comment Asymptotics of a function
The main contribution is around $i=n/(4\log n)$, not around $i=n$.
May
8
comment Asymptotics of a function
Which context did you meet this beast in?
May
8
comment Asymptotics of a function
$f(n)=n^{n+o(n)}$.
May
8
revised Probability distribution for two-state system that depends on residence time
added 386 characters in body; added 10 characters in body
May
8
revised Probability distribution for two-state system that depends on residence time
added 543 characters in body
May
8
comment Probability distribution for two-state system that depends on residence time
If $p_+(\ ,t)$ and $p_-(\ ,t)$ are probability distributions, so is $p(\ ,t)$ as a barycenter of these. (But the question is about fixing $x$ once and for all and working on $p(x,\ )$ from $p_-(x,\ )$ and $p_+(x,\ )$, actually.)
May
8
comment correlation for three variables?
Hardly MO stuff, please try more adapted fora.
May
8
comment compute the waiting time for a given pattern with Kac’s lemma
As explained by others, Kac's lemma describes the mean return time to some word w starting from w. On the other hand, for the hitting time of w one starts from the empty word. Hence the hitting time is almost surely at least as large as the return time, likewise for their means. The mean hitting and return times coincide if and only if no terminal strict subword of w is an initial subword of w. For example, for w=HHHTT they coincide but for w=HTHTH they do not since HTH is both terminal and initial.
May
8
revised Probability distribution for two-state system that depends on residence time
deleted 2 characters in body
May
8
comment Probability distribution for two-state system that depends on residence time
Could you confirm or infirm the Edit?
May
8
revised Probability distribution for two-state system that depends on residence time
added 479 characters in body; added 103 characters in body; added 24 characters in body
May
7
comment Probability distribution for two-state system that depends on residence time
The answer is referring very precisely to the model you described. If you are interested in a different dynamics, please explain clearly what it is. Alternatively, describe what you think the problem with the derivation above is, avoiding vague terms such as "the fact that p±(x,t) evolves with time" (of course it "evolves with time", otherwise what would the argument $t$ be there for?).
May
7
answered Probability distribution for two-state system that depends on residence time
May
6
answered Probability that one RV will exceed many others
May
6
comment Placing Bounds on Correlation/Covariance Through Correlation with an Intermediate Variable
Thus, if $c_{1,2}=c_{1,3}=0.99$, then $2(0.99)^2-1\leqslant c_{2,3}\leqslant1$ (and every value inbetween can be realized).
May
6
comment Closed form solution to an iterative equation.
Standard comparison to the associated differential equation yields $y(n)=\Theta(n^b)$ with $b=1/(1-a)$ (and, with some more care, much more precise estimates) but this is not a research question. You might want to try math.stackexchange.com instead.
May
3
comment Random graphs nonisomorphic to unit distance graphs
@Benoît But the homework factor.
May
1
awarded  Nice Question
Apr
30
revised Mathematicians whose works were criticized by contemporaries but became widely accepted later
deleted 2 characters in body
Apr
29
comment A sampling and learning question
See en.wikipedia.org/wiki/Mode_%28statistics%29.
Apr
29
comment A sampling and learning question
Try the mode of the results $b$.
Apr
29
comment Distribution of convex combination of i.i.d Gamma random variables
I have also posted this question... on a site where some objections to the first inequality were raised. Any follow-up on these?
Apr
29
comment Quadratic Variation and Distribution
I fail to see a question here, "the relation between distribution of $X_n$ and the process $S_n$" can mean about anything, no?
Apr
29
comment Intution behind conditional expectation when sigma algebra isn’t generated by a partition
Apparently simultaneously crossposted at MSE.
Apr
22
comment The first eigenvalue of a branching process matrix
Conditionally on non-extinction.
Apr
22
comment The first eigenvalue of a branching process matrix
if it is larger than 1, then there are types that won't get extinct... is not accurate: rather, there is a positive probability that some types will not get extinct.
Apr
10
accepted Integral of the product of Normal density and cdf
Apr
10
comment Integral of the product of Normal density and cdf
A faulty step is "At this point, given that" since when $B\to-\infty$, the product you consider goes to $\Phi(0)\phi(f)=\frac12\phi(f)\ne0$.
Apr
10
answered Integral of the product of Normal density and cdf
Mar
26
comment Is the Binomial Expectation of a Multivariate Convex Function Convex in the Vector p?
@Hugh The function $h$ defined by $h(x_1,x_2)=(1-x_1)+(1-x_2)+1$ is linear hence there is no counterexample there. If you mean $h(x_1,x_2)=(1-x_1)(1-x_2)+1$, then this is Victor's example modulo an irrelevant affine part.
Mar
25
comment Understanding Proof on paper “ is Pitmann Closeness a reasonable criterion"
And you really expect people to go and check what (2.1), (2.2), (2.3) and (2.4) are? Voting to close.
Mar
25
comment Minimum of exponential distributions
Hardly MO stuff. Voting to close.
Mar
18
revised Uniformly integrable sequence such that a.s. limit and conditional expectation do not commute
edited body
Mar
18
revised Uniformly integrable sequence such that a.s. limit and conditional expectation do not commute
edited title
Mar
17
awarded  Scholar
Mar
17
comment Compactness of sigma-algebra for the $L^1$ metrics
@Rabee Thanks. What do you call "not compact in $L^1$"? Which part of Dunford and Schwartz?
Mar
17
comment Compactness of sigma-algebra for the $L^1$ metrics
@Julien Thanks for this answer. To which probability measures on [0,1], apart from the Lebesgue measure, does this apply?
Mar
17
comment Ito formulae for stochastic processes with finite cubic, quartic … n-tic variation
You are welcome. Always better to have an answer by the experts... Would you suggest that the OP reads Errami and Russo 2003 BEFORE these other, more recent, references, or not necessarily so?
Mar
17
asked Compactness of sigma-algebra for the $L^1$ metrics
Mar
15
awarded  Yearling
Mar
13
comment Ito formulae for stochastic processes with finite cubic, quartic … n-tic variation
See ERRAMI M. and RUSSO F. (2003). n-covariation, generalized Dirichlet processes and calculus with respect to finite cubic variation processes. Stochastic Process. Appl. 104 259–299.
Feb
15
revised Convexity in $\{0,1\}^n$
added 6 characters in body; edited title; edited title
Jan
29
revised Journals for undergraduates
deleted 4 characters in body
Jan
29
revised Journals for undergraduates
deleted 1 characters in body
Jan
22
revised Expectation of random matrix inverse
added 5 characters in body; edited tags