Rushil Surti

rush040507@gmail.com


Description

My list of articles so far and this website's homepage. I primarily write about math and comp sci.

Articles


An Electromagnetism Cycloid

Author: Rushil Date: April 1, 2025 Tags: mini physics linear-algebra differential-equations complex-numbers

Not an April Fool's joke! This is a mini article on an electromagnetism problem mentioned in one of our class's textbooks. The exact solution was said to be beyond the scope of the textbook, so, don't mind if I do!

Music-Inspired Mathematics

Author: Rushil Date: March 21, 2025 Tags: fourier-transform signal-processing analysis linear-algebra

An orchestra assignment special! In this article, I explore the connection between music and math concretely. In particular, we'll take a look at some signal processing and some even more out there connections to springboard into some fun pure math.

Convolution Canonicity: Dirichlet Convolutions!

The primer article in a series exploring convolution in group theory. The topic? Dirichlet convolutions! We'll generalize them over arbitrary fields and classify some certain cases.

A Combinatorial Totient Sum Identity

Author: Rushil Date: December 21, 2024 Tags: mini combinatorics number-theory

A very small article before winter break, featuring a clean double counting argument for a sum involving the Euler totient function.

Project Euler: Problem 752

Author: Rushil Date: December 5, 2024 Tags: project-euler number-theory matrices abstract-algebra group-theory

Solving Project Euler Problem 752, a nice problem on orders in fields with square roots.

PUMAC Power Round 2024: The Hausdorff Measure

Author: Rushil Date: November 28, 2024 Tags: notes contest topology measure-theory

Notes on and a review of what our team managed to solve in PUMAC Power Round 2024! Featuring measure theory, topology, and fractals.

A Remark on Commuting Matrices

Author: Rushil Date: November 9, 2024 Tags: linear-algebra matrices

Suppose matrices \( A \) and \( B \) commute. We explore the question of when one matrix can be expressed in terms of the other.

Project Euler: Problem 421

Solving Project Euler Problem 421, a beautiful number theory puzzle on counting roots modulo primes with a cryptographic and probabilistic flavor.

Proving that the Euler Totient is Even

Author: Rushil Date: July 23, 2024 Tags: number-theory group-theory

We prove that the Euler totient function is even using group theory.

Codeforces: Problem 1916H1

Author: Rushil Date: July 21, 2024 Tags: codeforces linear-algebra matrices combinatorics number-theory

A very mathy and beautiful 2700 rated Codeforces problem. This one had me really excited to solve.

Matrices Over Modular Arithmetic

Author: Rushil Date: July 11, 2024 Tags: matrices linear-algebra number-theory combinatorics group-theory

Exploring properties of powers of matrices who have entries in the ring of integers modulo some integer.

Codeforces: Problem 1763D

Author: Rushil Date: July 5, 2024 Tags: codeforces combinatorics permutations

A 2200 rated Codeforces combinatorics problem with a whole lot of casework.

Binomial Coefficient Matrices

Author: Rushil Date: June 30, 2024 Tags: linear-algebra matrices combinatorics binomial-coefficient

Let's explore the properties of lower triangular matrices filled with binomial coefficients.

Project Euler: Problem 743

Author: Rushil Date: June 25, 2024 Tags: project-euler combinatorics matrices

Solving Project Euler Problem 743, a really nice combo problem using a sliding window approach.

Project Euler: Problem 779

Author: Rushil Date: June 23, 2024 Tags: project-euler number-theory analysis primes

Solving Project Euler Problem 779, a really beautiful number theory problem.

Perspective Projection

Author: Rushil Date: June 17, 2024 Tags: linear-algebra graphics

Developing a perspective projection for use in rendering 3D graphics. This particular derivation was used in my AP CSA final project :D

Drawing Equipotential Lines

Author: Rushil Date: June 9, 2024 Tags: physics linear-algebra multivariable-calculus

Deriving an algorithm to draw equipotential lines for a vector field starting from a point with lots of fun math along the way.

Project Euler: Problem 549

Author: Rushil Date: June 7, 2024 Tags: project-euler number-theory

Solving Project Euler Problem 549, a nice number theory problem revolving around the factorization of factorials.

Gradient Ascent Eigenvectors

Author: Rushil Date: May 13, 2024 Tags: linear-algebra matrices gradient-descent

Finding real eigenvectors of an arbitrary matrix using geometric intuition and gradient ascent.

Codeforces: Problem 1909D

Author: Rushil Date: April 7, 2024 Tags: codeforces number-theory optimization

A nice little 1900 rated Codeforces problem on making all elements equal with operations.

Yukicoder: Problem 2664

Author: Rushil Date: April 1, 2024 Tags: yukicoder graph-theory dfs number-theory

Solving Yukicoder Problem 2664, a quick little graph and number theory problem, with the extra challenge of having to read the problem description in Japanese.

Codeforces: Problem 1902C

Author: Rushil Date: March 24, 2024 Tags: codeforces number-theory optimization

A quick little number theory Codeforces problem on minimizing costs.

Codeforces: Problem 1948E

Author: Rushil Date: March 15, 2024 Tags: codeforces graph-theory number-theory permutations

A fun (slightly brute-force) constructive graph theory Codeforces problem, rated 2100.

Codeforces: Problem 1758D

Author: Rushil Date: March 9, 2024 Tags: codeforces number-theory

A nice 1800 rated Codeforces problem on constructing an integer sequence. Multiple attempts, because an initial strategy doesn't always work but is nice to document.

Project Euler: Problem 323

Author: Rushil Date: January 12, 2024 Tags: project-euler bitmasks probability

Solving Project Euler Problem 323, a fun problem involving bitwise OR and expected values.