Boyer-Moore

A Cartesian Tree is a binary tree that is uniquely defined by a sequence of numbers and has two key properties: it is a binary search tree (BST) with respect to the values of the nodes, and it is a min-heap with respect to the indices of the elements in the original sequence. This means that for any node $N$ in the tree, all values in the left subtree are less than $N$, and all values in the right subtree are greater than $N$. Additionally, if you were to traverse the tree in a pre-order manner, the sequence of values would match the original sequence's order of appearance.

To construct a Cartesian Tree from an array, one can use the following steps:

1. Select the Minimum: Find the index of the minimum element in the array.
2. Create the Root: This minimum element becomes the root of the tree.
3. Recursively Build Subtrees: Divide the array into two parts — the elements to the left of the minimum form the left subtree, and those to the right form the right subtree. Repeat the process for both subarrays.

This structure is particularly useful for applications in data structures and algorithms, such as for efficient range queries or maintaining dynamic sets.

The Gauss-Bonnet Theorem is a fundamental result in differential geometry that relates the geometry of a surface to its topology. Specifically, it states that for a smooth, compact surface $S$ with a Riemannian metric, the integral of the Gaussian curvature $K$ over the surface is related to the Euler characteristic $\chi(S)$ of the surface by the formula:

Here, $dA$ represents the area element on the surface. This theorem highlights that the total curvature of a surface is not only dependent on its geometric properties but also on its topological characteristics. For instance, a sphere and a torus have different Euler characteristics (1 and 0, respectively), which leads to different total curvatures despite both being surfaces. The Gauss-Bonnet Theorem bridges these concepts, emphasizing the deep connection between geometry and topology.

The Dirac Delta function, denoted as $\delta(x)$, is a mathematical construct that is not a function in the traditional sense but rather a distribution. It is defined to have the property that it is zero everywhere except at $x = 0$, where it is infinitely high, such that the integral over the entire real line equals one:

This unique property makes the Dirac Delta function extremely useful in physics and engineering, particularly in fields like signal processing and quantum mechanics. It can be thought of as representing an idealized point mass or point charge, allowing for the modeling of concentrated sources. In practical applications, it is often used to simplify the analysis of systems by replacing continuous functions with discrete spikes at specific points.

Price elasticity refers to the responsiveness of the quantity demanded or supplied of a good or service to a change in its price. It is a crucial concept in economics, as it helps businesses and policymakers understand how changes in price affect consumer behavior. The formula for calculating price elasticity of demand (PED) is given by:

A PED greater than 1 indicates that demand is elastic, meaning consumers are highly responsive to price changes. Conversely, a PED less than 1 signifies inelastic demand, where consumers are less sensitive to price fluctuations. Understanding price elasticity helps firms set optimal pricing strategies and predict revenue changes as market conditions shift.

Stochastic Gradient Descent (SGD) is an optimization algorithm used to minimize an objective function, typically in the context of machine learning. The fundamental idea behind SGD is to update the model parameters iteratively based on a randomly selected subset of the training data, rather than the entire dataset. This leads to faster convergence and allows the model to escape local minima more effectively.

Mathematically, at each iteration $t$, the parameters $\theta$ are updated as follows:

where $\eta$ is the learning rate, and $(x^{(i)}, y^{(i)})$ is a randomly chosen training example. Proofs of convergence for SGD typically involve demonstrating that, under certain conditions (like a diminishing learning rate), the expected value of the loss function will converge to a minimum as the number of iterations approaches infinity. This is crucial for ensuring that the algorithm is both efficient and effective in practice.

The Erdős Distinct Distances Problem is a famous question in combinatorial geometry, proposed by Hungarian mathematician Paul Erdős in 1946. The problem asks: given a finite set of points in the plane, how many distinct distances can be formed between pairs of these points? More formally, if we have a set of $n$ points in the plane, the goal is to determine a lower bound on the number of distinct distances between these points. Erdős conjectured that the number of distinct distances is at least $\Omega\left(\frac{n}{\log n}\right)$, meaning that as the number of points increases, the number of distinct distances grows at least proportionally to $\frac{n}{\log n}$.

The problem has significant implications in various fields, including computational geometry and number theory. While the conjecture has been proven for numerous cases, a complete proof remains elusive, making it a central question in discrete geometry. The exploration of this problem has led to many interesting results and techniques in combinatorial geometry.