## Electronic Journal of Probability

- Electron. J. Probab.
- Volume 24 (2019), paper no. 82, 22 pp.

### Optimizing the drift in a diffusive search for a random stationary target

#### Abstract

Let $a\in \mathbb{R} $ denote an unknown stationary target with a known distribution $\mu \in \mathcal{P(\mathbb {R}} )$, the space of probability measures on $\mathbb{R} $. A diffusive searcher $X(\cdot )$ sets out from the origin to locate the target. The time to locate the target is $T_{a}=\inf \{t\ge 0: X(t)=a\}$. The searcher has a given constant diffusion rate $D>0$, but its drift $b$ can be set by the search designer from a natural admissible class $\mathcal{D} _{\mu }$ of drifts. Thus, the diffusive searcher is a Markov process generated by the operator $L=\frac{D} {2}\frac{d^{2}} {dx^{2}}+b(x)\frac{d} {dx}$. For a given drift $b$, the expected time of the search is \[ \int _{\mathbb{R} } (E^{(b)}_{0}T_{a})\thinspace \mu (da).\tag{0.1} \] Our aim is to minimize this expected search time over all admissible drifts $b\in \mathcal{D} _{\mu }$. For measures $\mu $ that satisfy a certain balance condition between their restriction to the positive axis and their restriction to the negative axis, a condition satisfied, in particular, by all symmetric measures, we can give a complete answer to the problem. We calculate the above infimum explicitly, we classify the measures for which the infimum is attained, and in the case that it is attained, we calculate the minimizing drift explicitly. For measures that do not satisfy the balance condition, we obtain partial results.

#### Article information

**Source**

Electron. J. Probab., Volume 24 (2019), paper no. 82, 22 pp.

**Dates**

Received: 12 September 2018

Accepted: 18 June 2019

First available in Project Euclid: 10 September 2019

**Permanent link to this document**

https://projecteuclid.org/euclid.ejp/1568080861

**Digital Object Identifier**

doi:10.1214/19-EJP335

**Mathematical Reviews number (MathSciNet)**

MR4003135

**Zentralblatt MATH identifier**

07107389

**Subjects**

Primary: 60J60: Diffusion processes [See also 58J65]

**Keywords**

random target diffusive search drift optimization

**Rights**

Creative Commons Attribution 4.0 International License.

#### Citation

Pinsky, Ross G. Optimizing the drift in a diffusive search for a random stationary target. Electron. J. Probab. 24 (2019), paper no. 82, 22 pp. doi:10.1214/19-EJP335. https://projecteuclid.org/euclid.ejp/1568080861