Uploaded August 2021 | Updated September 2026, 2 days ago
This video goes over a fun little problem from A Hilbert Space Problem Book by Paul Halmos. It's a simple problem to understand, and the solution to it is surprisingly deep. It allows us to introduce the idea of a Reproducing Kernel Hilbert Space through what are called Generating Functions. The prerequisite for this is primarily a knowledge of power series and some linear algebra. I try to build up what I can in the first few minutes, which lets us get to some more advanced ideas. Ultimately we are talking about a connection between sequences, Hilbert Spaces, generating functions, complex analysis, and the Hardy space.
Since 3blue1brown is running his Summer of Mathematical Exposition, I thought I'd go with a bit more of an accessible topic this time. That's also the plan for the future, where I will mix in research, graduate, and undergraduate work into my channel content. As I said before, this one is aimed at someone who has had Calculus 2 and some Linear Algebra. Experience with complex analysis will help, but all we need from there are power series (analytic functions).
Music:
Go on - Cacti
Come 2gether - Ooyy
Try Once More - Ben Elson
Video Call from Los Angeles - Trevor Kowalski
Disque Magique - Dusty Decks
I Know Now - Cacti
Wrong - Dan Henig
Guardians + Tek - Craig Hardgrove
#summerofmathexposition
This video goes over a fun little problem from A Hilbert Space Problem Book by Paul Halmos. It's a simple problem to understand, and the solution to it is surprisingly deep. It allows us to introduce the idea of a Reproducing Kernel Hilbert Space through what are called Generating Functions. The prerequisite for this is primarily a knowledge of power series and some linear algebra. I try to build up what I can in the first few minutes, which lets us get to some more advanced ideas. Ultimately we are talking about a connection between sequences, Hilbert Spaces, generating functions, complex analysis, and the Hardy space.
Since 3blue1brown is running his Summer of Mathematical Exposition, I thought I'd go with a bit more of an accessible topic this time. That's also the plan for the future, where I will mix in research, graduate, and undergraduate work into my channel content. As I said before, this one is aimed at someone who has had Calculus 2 and some Linear Algebra. Experience with complex analysis will help, but all we need from there are power series (analytic functions).
Music:
Go on - Cacti
Come 2gether - Ooyy
Try Once More - Ben Elson
Video Call from Los Angeles - Trevor Kowalski
Disque Magique - Dusty Decks
I Know Now - Cacti
Wrong - Dan Henig
Guardians + Tek - Craig Hardgrove
#summerofmathexposition






![Getting caught with facial recognition - How SVDs are used in Facial Recognition Software
This video builds on the SVD concepts of the previous videos, where I talk about the algorithm from the paper Eigenfaces for Recognition. These tools are used everywhere from law enforcement (such as tracking down the rioters at the Capitol) to unlocking your cell phone.
Followup Video: https://youtu.be/WnsKGBy1PXQ
Music:
Come 2gether by Ooyy
Guardians + Tek by Craig Hardgrove
Images:
Lectern Photo by Win McNamee/Getty Images (Used under Fair Use for an educational video)
Face Data obtained from http://www.databookuw.com/ the readme states
This data is modified from the Extended Yale Face Database B. If using this data, please also cite the following two papers:
[1] A. S. Georghiades, P. N. Belhumeur, and D. J. Kriegman, From few to many: Illumination cone models for face recognition under variable lighting and pose, IEEE Trans. Pattern Anal. Mach. Intell., 23 (2001), pp. 643–660.
[2] K. Lee, J. Ho, and D. J. Kriegman, Acquiring linear subspaces for face recognition under variable lighting, IEEE Trans. Pattern Anal. Mach. Intell., 27 (2005), pp. 684–698.
Link to website: vision.ucsd.edu/content/extended-yale-face-database-b-b Getting caught with facial recognition - How SVDs are used in Facial Recognition Software](https://i.ytimg.com/vi/b-5jg5VvUEo/mqdefault.jpg)



