# Björn Engquist

The University of Texas at Austin

201 E. 24th Street, 1 University Station, Austin, Texas 78712-1229

ArXiv: *Numerical methods for multiscale inverse problems* (January 2014)

CV

Homepage

Twitter

Wikipedia

YouTube: *Basis in Information Theory*

References within this website:

https://81018.com/e8/#Björn

This page is https://81018.com/2019/04/18/engquist/

First email: 18 April 2019

Dear Prof. Dr. Björn Engquist:

Not being a scholar or expert, I am still fascinated with your work to define the development of absorbing boundary conditions.

We began our work in a high school geometry class where we were observing how an octahedron is in the center of a tetrahedron with half-sized tetrahedrons in each corner. Within the octahedron, there is a half-sized octahedron in each of the six corners and a tetrahedron in each of the eight faces all sharing the centerpoint.

We decided to do a Zeno-like progression and applied base-2 going back deeper and deeper inside. In 45 steps we were in the range of particle physics, and in another 67 steps we were in the range of Planck’s base units.

We then decided to multiply by 2 and in 90 steps we were in the range of the age and size of the universe.

For high school people, it was great fun. We encapsulated the universe in 202 steps. We only then found Kees Boeke’s work and began thinking of the differences between base-10 and base-2.

I suspect that you are one of the few people on earth who has thought very deeply about computational multi-scale methods. Might you advise us? Are we being illogical? Are we doing something wrong? Thank you.

Most sincerely,

Bruce

**Links above**:

https://81018.com/chart/

https://81018.com/home/

https://81018.com/tot/

https://81018.com

**Current research**:

https://people.maths.ox.ac.uk/trefethen/6all.pdf

https://www.encyclopediaofmath.org/index.php/Absorbing_boundary_conditions

https://math.mcgill.ca/gantumur/docs/down/Engquist77.pdf