Krzysztof Sakrejda

Northampton, Massachusetts, United States

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Summary

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Krzysztof Sakrejda is an applied statistician and software engineer with 11 years of experience building production-ready data pipelines and Bayesian models that inform high-stakes decision making in public health and clinical trials. He implements and deploys complex probabilistic models in Stan—contributing substantive back-end and testing work to prominent open-source projects like stan, rstan, and the Stan Math Library—bringing deep expertise in sparse matrix operations and numerical robustness. His decade-plus academic career produced operational data systems (multi-decade surveillance databases) and novel small-area and reporting-delay models that improved epidemic forecasting and guided Thai public health responses. At Generable he combined patient-level RCT data ingestion with a Bayesian joint survival–biomarker model to enable cross-trial inference and quantitative go/no-go frameworks. Comfortable translating technical uncertainty for non-technical stakeholders, he routinely delivers concise model summaries that support practical decisions. Based in Northampton, MA, he blends rigorous scientific training (PhD in Organismic & Evolutionary Biology) with pragmatic software engineering to move models from research to reliable production use.

11 years of coding experience

5 years of employment as a software developer

University of Oregon

Bachelor of Arts (B.A.), Chemistry, Bachelor of Arts (B.A.), Chemistry at Vassar College

University of Massachusetts Amherst

Github Skills (19)

bayesian-statistics10

c-language10

bayesian-data-analysis10

r-package10

r10

testing10

mathematics10

sparse-matrix10

math10

bayesian10

eigen10

statistical-models10

rcpp10

bayesian-methods10

stan10

Programming languages (8)

TypeScriptC++RCRustJavaScriptHTMLPython

Github contributions (5)

stan-dev/math

Mar 2015 - Oct 2020

The Stan Math Library is a C++ template library for automatic differentiation of any order using forward, reverse, and mixed modes. It includes a range of built-in functions for probabilistic modeling, linear algebra, and equation solving.

Role in this project:

Backend Developer

Contributions:8 reviews, 142 commits, 17 PRs in 5 years 8 months

Contributions summary:Krzysztof primarily contributed to the development of the Stan Math Library by implementing and integrating new functionality. The commits focused on the addition of the `sparse_multiply` function, including both CSC and CSR versions, and the associated error checking, demonstrating a solid understanding of sparse matrix operations and integration of new functions within the existing library structure. Furthermore, the commits involved refactoring code to fit the library's hierarchy. Additionally, test cases were created to ensure correctness of the new functions and their functionalities.

automatic-differentiationprobabilistic-modelingsundialsmodestemplate-library

stan-dev/rstan

Sep 2015 - Aug 2018

RStan, the R interface to Stan

Role in this project:

Back-end Developer

Contributions:15 commits, 2 PRs, 12 pushes in 2 years 11 months

Contributions summary:Krzysztof primarily focused on enhancing the RStan interface to Stan, particularly concerning sparse matrix functionalities and the integration of random number generators. They implemented and refactored code related to extracting sparse components and exposed functions. Their contributions also involved improvements to the underlying C++ code and the interaction between R and Stan, including updates to the exporter and related header files. The user also created supporting functions related to random number generators.

r-packagebayesian-inferencestanrstanrstats

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