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Factor Covariance EMA Update

Medium · risk_management · Quant Researcher interview question · risk-management, covariance, ema, factor-models, numpy

Exponential moving average (EMA) covariance matrices are fundamental in risk management for their efficient, recursive updates. This allows for real-time tracking of factor risk in streaming data environments without storing an entire history of returns. The decay factor lam controls the memory of the estimator, balancing responsiveness to new information against stability. Task Implement solution(cov0: list, returns: list, lam: float) -> list to update a factor covariance matrix using the expo