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This is a medium difficulty Statistics & Math question, commonly asked during Technical Screen rounds at Other.

What role is this question designed for?

This question is commonly asked for Data Scientist candidates at Other during technical interviews.

Compute and estimate Markov transition probabilities

Quick Overview

This question evaluates understanding of discrete-time Markov chains, multi-step transition probabilities and empirical estimation of transition matrices, testing probabilistic reasoning and matrix-based computation in the Statistics & Math domain for a Data Scientist role; it is commonly asked because it probes both theoretical grasp of stochastic processes and practical data-driven parameter estimation. At an applied algorithmic abstraction level, it requires explicit mapping of state labels to matrix indices, computing k-step transitions from a given row-stochastic matrix, estimating transition probabilities from observed one-step transitions, and addressing zero-outgoing-observation cases and any chosen smoothing policy (or justification for none).

A system is modeled as a discrete-time Markov chain over m states S = {s1, s2, ..., sm}.

Part A (multi-step probabilities):

You are given a row-stochastic transition matrix P of shape (m x m) , where P[i][j] = P(X_{t+1}=sj | X_t=si) .
For several queries (start_state=a, end_state=b, steps=k) , compute P(X_{t+k}=b | X_t=a) .

Part B (estimate transition matrix from observations):

You are given a list of observed one-step transitions, e.g. [(s1,s2), (s2,s3), (s1,s3), (s1,s2), ...] .
Estimate the transition probability matrix \hat{P} using empirical transition frequencies.

Requirements/notes:

Clearly define how you map state labels to matrix indices.
Handle states that may have zero outgoing observations in Part B.
State any smoothing you choose (or justify not using smoothing).

Quick Overview

A system is modeled as a discrete-time Markov chain over m states S = {s1, s2, ..., sm}.

Part A (multi-step probabilities):

You are given a row-stochastic transition matrix P of shape (m x m) , where P[i][j] = P(X_{t+1}=sj | X_t=si) .
For several queries (start_state=a, end_state=b, steps=k) , compute P(X_{t+k}=b | X_t=a) .

Part B (estimate transition matrix from observations):

You are given a list of observed one-step transitions, e.g. [(s1,s2), (s2,s3), (s1,s3), (s1,s2), ...] .
Estimate the transition probability matrix \hat{P} using empirical transition frequencies.

Requirements/notes:

Clearly define how you map state labels to matrix indices.
Handle states that may have zero outgoing observations in Part B.
State any smoothing you choose (or justify not using smoothing).

Compute and estimate Markov transition probabilities

Quick Overview

Solution

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Compute and estimate Markov transition probabilities

Quick Overview

Solution

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