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Theory and applications of probability and stochastic processes: e.g. central limit theorems, large deviations, stochastic differential equations, models from statistical mechanics, queuing theory.

6 votes

Moments of a positive random variable

This is known as the truncated Stieltjes moment problem, and there is a necessary and sufficient condition taking the form of a semidefinite program. See Section 5 of the classic paper by Curto and Fi …
Tobias Fritz's user avatar
  • 6,406
8 votes

Why Kleisli Markov categories and not the Eilenberg-Moore categories of the associated monads

What can you do with the Kleisli category (of a probability monad) that you can't do with the Eilenberg-Moore category? The first paragraph of kirk sturtz's answer provides a good high-level summary …
Tobias Fritz's user avatar
  • 6,406
23 votes
2 answers
1k views

How large can $\mathbf{P}[X_1 + X_2 + X_3 < 2 X_4]$ get?

Let $\mu$ be a probability measure on $[0,\infty)$ and $X_1, \dots, X_4 \sim \mu$ independent. Then what can be said about the probability that $X_1 + X_2 + X_3 < 2 X_4$? More precisely, what is the v …
Tobias Fritz's user avatar
  • 6,406
4 votes

How large can $\mathbf{P}[X_1 + X_2 + X_3 < 2 X_4]$ get?

In this answer, I will derive the following improved bounds: $$0.367 \approx \frac{208}{567} \le \sup_\mu \mathbf{P}[X_1 + X_2 + X_3 < 2 X_4] \le \frac{7}{15} \approx 0.467.$$ In the remarks at the en …
Tobias Fritz's user avatar
  • 6,406
2 votes

General additive function of probability

Here is a partial answer. As has been hinted at in the comments, one should expect that the space of functions under question strongly depends on the continuity assumption made. For example, the Rényi …
Tobias Fritz's user avatar
  • 6,406
7 votes
1 answer
383 views

Idempotent splitting for Markov kernels

Let $X$ be a standard Borel space and $e : X \to X$ a Markov kernel. Suppose that $e$ is idempotent, that is $e \circ e = e$, or written out using the Chapman-Kolmogorov equation, $$e(A|x) = \int_X e( …
Tobias Fritz's user avatar
  • 6,406
2 votes
0 answers
172 views

When should the empirical measure of an infinite sequence be defined?

Let $(x_n)_{n \in \mathbb{N}}$ be a (deterministic) sequence of nonnegative reals, possibly even with $x_n \in \mathbb{N}$ if you prefer. Then we'd like to define the empirical measure of such a seque …
Tobias Fritz's user avatar
  • 6,406
7 votes
Accepted

Hopf monads in categorical probability theory

Since the idea of a probability monad is not a fully formal concept, there can be no fully formal answer to this question. Nevertheless, I will argue below that no nontrivial probability monad is a Ho …
Tobias Fritz's user avatar
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