Jeff Armstrong - President at Approximatrix, LLC

Jeff Armstrong

President at Approximatrix, LLC

Westlake, Ohio, United States

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Summary

🤩

Rockstar

🎓

Top School

Jeff Armstrong is a technically deep president and principal developer with 15+ years building numerical and scientific software, blending expertise in CFD, econometrics, multithreading and low-level systems in languages from Fortran and C to Java and Python. As founder of Approximatrix he has translated advanced math and control theory into production-grade code for aerospace and controls applications, and contributed substantive backend improvements to high-profile open-source projects such as SciPy and Open Watcom (including Schur decomposition sorting, discrete LTI support, and C99 math functions). He is comfortable across the stack of algorithm design, LAPACK integration and signal-processing tooling, and has a track record of adding rigorous tests and numerical solvers like TRSYL to shared libraries. With graduate training in mechanical engineering and economics and hands-on aerospace experience, he combines theoretical rigor with practical engineering judgment. Based in Westlake, Ohio, he also brings unconventional leadership lessons from coaching high-school varsity soccer, reflecting a collaborative, mentoring approach to technical teams.

15 years of coding experience

10 years of employment as a software developer

MS, Mechanical Engineering, MS, Mechanical Engineering at Case Western Reserve University

MA, Economics, MA, Economics at Cleveland State University

Github Skills (14)

algorithms10

scipy10

c-programming10

python10

linear-algebra10

scientific-computing10

signal-processing10

numpy10

compiler-development10

lapack9

error-handling9

data-analysis8

posixct7

posix7

Programming languages (8)

TypeScriptShellC++CM4RubyFortranPython

Github contributions (5)

open-watcom/open-watcom-v2

Oct 2013 - Jan 2023

Open Watcom V2.0 - Source code repository, Wiki, Latest Binary build, Archived builds including all installers for download.

Role in this project:

Back-end Developer

Contributions:142 commits, 22 PRs, 31 pushes in 9 years 5 months

Contributions summary:Jeff primarily focused on enhancing the Open Watcom C/C++ compiler's math library by implementing new math functions, including the error function (erf), complementary error function (erfc), and the logarithm of the gamma function (lgamma). They also worked on improving the existing library by fixing errors and ensuring compatibility with both 16-bit and 32-bit targets. Furthermore, they added new functions such as remquo, and incorporated C99 math error handling and standard library functions.

watcom

scipy/scipy

Apr 2011 - Feb 2012

SciPy library main repository

Role in this project:

Backend Developer & Data Scientist

Contributions:9 commits, 1 comment in 10 months

Contributions summary:Jeff implemented features for the Schur decomposition routine, adding sorting functionality based on eigenvalue properties, as well as fixes to existing code. They added zeros-poles-gain support to discrete LTI functions, enabling new representations and functionality. The user also enhanced the signal processing module, adding discrete LTI systems, and continuous-to-discrete transforms. They further exposed LAPACK's TRSYL Sylvester equation solver and added tests.

scipypythonscientific-computing

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