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Stochastic Models
Stochastic Learning StudioBeta
1.1Symmetric Random Walk1.2Rescaled Random Walk1.3Standard deviation1.4Central Limit Theorem2.1Defining the Wiener process2.2Increment explorer2.3Joint distributions and covariance3.1Running maximum and minimum3.2Reflection principle3.3First passage times3.4Hitting probabilities
Brownian MotionBeta
Geometric Brownian MotionBeta
Itô ProcessBeta
Monte CarloBeta

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Stochastic Models

An interactive learning path from random walks to financial applications.

  1. Random walk
  2. Continuous limit
  3. Wiener process
  4. Itô calculus
  5. SDEs
  6. Applications
11 / 14 lessons in the studio
01

Chapter 1 · Discrete to Continuous

From the discrete random walk to continuous Brownian motion.

  • 1.1Symmetric Random WalkSums of independent ±1 steps; variance growth and the endpoint distribution.Open
  • 1.2Rescaled Random WalkRescaling the walk by √n and the Brownian limit (Donsker's principle).Open
  • 1.3Standard deviationHow fast does a random walk spread out? The empirical std converges to √t.Open
  • 1.4Central Limit TheoremHow sums of independent variables lead to the normal distribution.Open
02

Chapter 2 · Brownian Motion Fundamentals

Defining the Wiener process, its increments and covariance.

  • 2.1Defining the Wiener processThe four defining properties, and why paths are continuous yet nowhere differentiable.Open
  • 2.2Increment explorerPick a window [s, t]: the increment is N(0, t − s) wherever the window sits.Open
  • 2.3Joint distributions and covarianceW(s) and W(t) are jointly Gaussian with Cov = min(s, t); increments are independent.Open
  • 2.4Brownian transformations and invarianceScaling, sign symmetry, time reversal and time inversion — identities in distribution.Planned
  • 2.5Quadratic variationΣ(ΔW)² → T while total variation is infinite — the bridge into Itô calculus.Planned
  • 2.6Brownian bridgeBrownian motion conditioned on its endpoint: mean path and variance t(T − t)/T.Planned
Open Brownian Motion lab→
03

Chapter 3 · Brownian Path Geometry

Running maximum, the reflection principle and first passage times.

  • 3.1Running maximum and minimumInteractive simulation of the running maximum and minimum of Brownian motion, and why M(t) has the same law as |W(t)|.Open
  • 3.2Reflection principleThe reflection principle for Brownian motion, animated and checked by Monte Carlo: P(M(T) ≥ a) = 2·P(W(T) ≥ a).Open
  • 3.3First passage timesFirst passage times of Brownian motion: the Lévy density, its heavy tail and infinite mean, in an interactive simulation.Open
  • 3.4Hitting probabilitiesBarrier-hitting probabilities with drift and discrete monitoring, plus the BGK correction — the basis of barrier option pricing.Open
04

Chapter 4 · Stochastic Integration and Itô Calculus

Stochastic integration, the Itô isometry and Itô's lemma.

Open Itô Process lab→

Structured lessons planned; the standalone lab is available meanwhile.

05

Chapter 5 · Stochastic Differential Equations

Arithmetic and geometric Brownian motion, Euler–Maruyama, mean reversion.

Open Geometric Brownian Motion lab→

Structured lessons planned; the standalone lab is available meanwhile.

06

Chapter 6 · Advanced Concepts

Martingales, stopping times, filtrations and Girsanov's theorem.

Planned

This chapter is still in development.

07

Chapter 7 · Monte Carlo Laboratory

A general-purpose simulation laboratory and financial applications.

Open Monte Carlo lab→

Structured lessons planned; the standalone lab is available meanwhile.

About this tool

A hands-on course in stochastic processes and stochastic calculus. Each lesson poses a question and lets you answer it by experiment: from the symmetric random walk and the √t scaling law, through the central limit theorem and Donsker's theorem, to the Wiener process, its increments and covariance, the running maximum, the reflection principle and first passage times.

Frequently asked questions

Do I need to know stochastic calculus beforehand?

No. The lessons start from coin flips and build up step by step; each one has an Explore tab with experiments and a Mathematics tab with the precise statements.

Why does Brownian motion scale with √t?

Its increments over disjoint intervals are independent, so their variances add. Variance therefore grows linearly in time and the typical deviation, the standard deviation, grows like √t.