Skip to content
Free standard shipping to supported destinations
Delta-Xi LogoDelta Xi
ShopOur storyLearnHelp
Learn
OverviewConcepts
Delta-Xi LogoDelta Xi

A place for good ideas, on a shirt or off the page.

Say hello

Explore

  • Shop all
  • Mathematics T-shirts
  • Accessories
  • Learn
  • Our story

Here to help

  • Contact
  • Size & care questions
  • Shipping & returns
  • Your orders
  • Track an order

Keep in touch

  • Instagram
  • Discord
  • Telegram
  • Affiliate programme

© 2026 Delta Xi. Prices in USD.

PrivacyTerms

Your cookie choices

Essential cookies keep your basket and sign-in working. Optional cookies help us understand visits and measure ads. Privacy details.

STEM Concepts

Follow an equation, work through an example, or check an assumption. Browse 69 concepts across mathematics, physics and computing.

All📐Mathematics(19)⚛️Physics(12)🔄Algorithms(7)🏗️Data Structures(8)🤖Machine Learning(10)🧠CS Theory(5)🖥️Systems(2)🌐Networking(3)⚙️Engineering(2)🧪Chemistry(1)

📐Mathematics(19)

View all
P(A∣B)=P(B∣A)P(A)P(B)P(A\mid B)=\frac{P(B\mid A)P(A)}{P(B)}P(A∣B)=P(B)P(B∣A)P(A)​

⚛️Physics(12)

View all
S=k_B\ln\Omega

🔄Algorithms(7)

View all
🔄

theory

Algorithms

Big O Notation

A mathematical notation that describes the limiting behavior of a function when the argument tends towards infinity.

View Explanation
🔄

algorithm

Algorithms

Binary Search

Search algorithm that finds the position of a target value within a sorted array in O(log n) time.

🏗️Data Structures(8)

View all
🏗️

data-structure

Data Structures

Binary Search Tree

Binary tree that maintains sorted order for efficient search, insert, and delete operations.

View Explanation
🏗️

data-structure

Data Structures

Binary Tree

🤖Machine Learning(10)

View all
🤖

theory

Machine Learning

Attention Mechanism

Technique that allows models to focus on relevant parts of the input sequence.

View Explanation
🤖

algorithm

Machine Learning

🧠CS Theory(5)

View all
🧠

theory

CS Theory

Halting Problem

The undecidable problem of determining whether a program will finish or run forever.

View Explanation
🧠

theory

CS Theory

NP-Completeness

Class of problems that are both in NP and NP-hard, representing the hardest problems in NP.

View Explanation

🖥️Systems(2)

View all
🖥️

theory

Systems

ACID Properties

Set of properties guaranteeing reliable database transactions: Atomicity, Consistency, Isolation, Durability.

View Explanation
🖥️

theory

Systems

CAP Theorem

States that a distributed system can only guarantee two of: Consistency, Availability, Partition tolerance.

🌐Networking(3)

View all
🌐

system

Networking

Domain Name System (DNS)

Hierarchical naming system that translates domain names to IP addresses.

View Explanation
🌐

system

Networking

HTTP Protocol

Application layer protocol for distributed, collaborative hypermedia information systems.

⚙️Engineering(2)

View all
Z=R+jX

🧪Chemistry(1)

View all
pV=nRT
Mathematics

Bayes' theorem

Update a probability when new evidence arrives.

View Explanation
n(Xˉn−μ)σ→dN(0,1)\frac{\sqrt{n}(\bar X_n-\mu)}{\sigma}\xrightarrow{d}N(0,1)σn​(Xˉn​−μ)​d​N(0,1)
Mathematics

Central limit theorem

Why averages can look normal even when individual observations do not.

View Explanation
I=\int_a^b f(x)\,dx
Mathematics

Definite Integral

Calculate the area under a curve between two points

View Explanation
f'(x)=\lim_{h \to 0} \frac{f(x+h)-f(x)}{h}
Mathematics

Definition of Derivative

The instantaneous rate of change of a function

View Explanation
Physics

Boltzmann Entropy

Connects microscopic states to thermodynamic entropy

View Explanation
Wt−Ws∼N(0,t−s),0≤s<tW_t-W_s\sim N(0,t-s),\qquad 0\le s<tWt​−Ws​∼N(0,t−s),0≤s<t
Physics

Brownian motion

A continuous random path with independent Gaussian increments.

View Explanation
\lambda = \frac{h}{p}
Physics

de Broglie Wavelength

Matter has wave-like properties at quantum scales

View Explanation
u(t)=e^{-t/\tau}
Physics

Exponential Decay

How quantities decrease over time (radioactivity, capacitors)

View Explanation
View Explanation
🔄

algorithm

Algorithms

Dijkstra's Algorithm

Finds the shortest paths between nodes in a weighted graph.

View Explanation
🔄

theory

Algorithms

Dynamic Programming

Method for solving complex problems by breaking them down into simpler overlapping subproblems.

View Explanation

Hierarchical data structure in which each node has at most two children.

View Explanation
🏗️

data-structure

Data Structures

Graph

Non-linear data structure consisting of vertices (nodes) connected by edges.

View Explanation
🏗️

data-structure

Data Structures

Hash Table

Data structure that implements an associative array with O(1) average lookup time.

View Explanation

Backpropagation

Algorithm for training neural networks by computing gradients through the chain rule.

View Explanation
🤖

theory

Machine Learning

Backtest leakage

When a historical test uses information unavailable at the time.

View Explanation
\theta := \theta - \alpha \nabla_\theta J(\theta)
Machine Learning

Gradient Descent Update

How neural networks learn by following the slope

View Explanation
🧠

theory

CS Theory

P vs NP Problem

The most important open problem in computer science: can every quickly verifiable solution be quickly found?

View Explanation
H(X)=−∑xp(x)log⁡2p(x)H(X)=-\sum_x p(x)\log_2 p(x)H(X)=−x∑​p(x)log2​p(x)
CS Theory

Shannon entropy

Measure uncertainty in a set of possible messages.

View Explanation
View Explanation
View Explanation
🌐

system

Networking

TCP/IP Protocol

Fundamental communication protocol suite that powers the internet.

View Explanation
Engineering

Complex Impedance

Resistance and reactance in AC circuits

View Explanation
V=IR
Engineering

Ohm's Law

Voltage equals current times resistance in circuits

View Explanation
Chemistry

Ideal Gas Law

Relates pressure, volume, and temperature of gases

View Explanation