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Use model variables named "sigma" as standard deviations rather than variances #296

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merged 2 commits into from
Jan 7, 2024

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Closes #295

Variables named "sigma" in structural models, as well as SARIMAX, were being directly inserted into the state/observation covariance matrix as-is. This implies they are variances, while the name "sigma" suggests they are standard deviations.

This PR squares parameters named "sigma" before inserting them into the appropriate covariance matrices to avoid surprising users due to incorrect naming convention.

@jessegrabowski jessegrabowski changed the title Model variables named "sigma" incorrectly expect variances Use model variables named "sigma" as standard deviations rather than variances Jan 5, 2024
@ricardoV94 ricardoV94 added bug Something isn't working major labels Jan 7, 2024
@jessegrabowski jessegrabowski merged commit 8dff969 into pymc-devs:main Jan 7, 2024
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@jessegrabowski jessegrabowski deleted the fix-sigma branch January 7, 2024 00:48
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Standard deviation parameters are incorrectly treated as variances in statespace covariance matrices
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