Compute Markov steady state and expectations

Quick Overview

Compute Markov steady state and expectations evaluates statistical assumptions, formulas, estimation strategy, uncertainty, edge cases, and interpretation in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

Compute Markov steady state and expectations

Company: DRW

Role: Data Scientist

Category: Statistics & Math

Difficulty: medium

Interview Round: Onsite

Answer the following probability/statistics sub-questions: 1) Given a finite-state, irreducible, aperiodic Markov chain with transition matrix P (provided), compute its stationary distribution π by solving πP = π with ∑i πi = 1, and state why the solution is unique. 2) Let X ~ Exponential(λ) and N ~ Poisson(λ), with λ > 0. Derive E[X] and E[N] from first principles (integration/summation), showing intermediate steps. 3) For a 2×2 zero-sum game with payoff matrix to Player A given in the prompt, find the mixed-strategy Nash equilibrium and report the probability each player assigns to their first action (use probability calculations to justify the equilibrium).

Quick Answer: Compute Markov steady state and expectations evaluates statistical assumptions, formulas, estimation strategy, uncertainty, edge cases, and interpretation in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

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Jul 28, 2025, 12:00 AM
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Compute Markov steady state and expectations

Probability and Game Theory: Three Sub-questions

Context: The exact transition matrix P (for Q1) and the 2×2 payoff matrix (for Q3) are not provided. Below, you will (a) solve generically in symbolic form, and (b) see a small numeric example to illustrate the procedure.

  1. Finite-state Markov chain
  • Given a finite-state, irreducible, aperiodic Markov chain with transition matrix P, compute its stationary distribution π by solving πP = π with ∑ᵢ πᵢ = 1. Explain why the solution is unique.
  1. Expectations from first principles
  • Let X ~ Exponential(λ) and N ~ Poisson(λ) with λ > 0. Derive E[X] and E[N] from first principles (integration/summation), showing intermediate steps.
  1. 2×2 zero-sum game
  • For a 2×2 zero-sum game with Player A’s payoff matrix [ [a, b], [c, d] ], find the mixed-strategy Nash equilibrium. Report the probability each player assigns to their first action (row 1 for A, column 1 for B), and justify the equilibrium with probability calculations.

Clarifying Questions to Ask Guidance

  • Clarify the random variables, distributional assumptions, independence assumptions, and desired output.
  • Show enough derivation for the interviewer to follow the reasoning.
  • Explain how you would validate the result with simulation or sensitivity checks.

What a Strong Answer Covers Guidance

  • A correct setup with definitions, formulas, and boundary conditions.
  • A step-by-step derivation or estimation plan.
  • Interpretation of the result, including uncertainty and practical limitations.
  • Checks for assumptions, edge cases, and numerical stability.

Follow-up Questions Guidance

  • How would the result change if the assumptions were relaxed?
  • Can you verify the answer with a simulation?
  • What is the most likely source of estimation error?
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