The user wants a Gray-Scott reaction-diffusion simulation in a single HTML file. This is a classic mathematical model that produces beautiful organic patterns resembling biological processes like membrane patterns, coral growth, etc.

Let me create a self-contained HTML file with:
1. A canvas element for rendering
2. The Gray-Scott algorithm implemented in JavaScript
3. Real-time animation loop
4. Mouse interaction to seed new growth
5. All CSS and JS inline

The Gray-Scott algorithm involves two coupled partial differential equations:
- ∂u/∂t = Du∇²u - uv² + F(1-u)
- ∂v/∂t = Dv∇²v + uv² - (F+k)v

Where:
- u is the concentration of one chemical
- v is the concentration of the other
- Du and Dv are diffusion rates
- F is the feed rate
- k is the kill rate

For the typical "coral" pattern that appears around F=0.055 and k=0.062, we seed the center with a small amount of v.

I'll create this with:
- A canvas that fills the screen
- Mouse movement adds v (the activator) to create patterns
- The simulation runs in real-time
- Beautiful organic colors based on v concentration

Let me write this complete HTML file.

I'll create a single-file Gray-Scott reaction-diffusion simulation with organic patterns and mouse seeding. Let me build this complete web app.

I've created a complete single-page web app that implements the Gray-Scott reaction-diffusion simulation. Let me verify it works correctly by checking the structure.

I've created a complete Gray-Scott reaction-diffusion simulation in `index.html`. The app features: **Core Features:** - **Real-time simulation** using the coupled partial differential equations that create organic Turing patterns - **Mouse seeding** - move your mouse to seed new growth patterns that evolve into beautiful cellular structures - **Click interaction** - click anywhere to add concentrated growth bursts **Controls Panel:** - **Feed Rate (F)** - controls the rate at which material is added to the system - **Kill Rate (k)** - controls the rate at which material is removed - **Diffusion rates (Du, Dv)** - control how quickly chemicals spread **Color System:** - Dark blue → Purple → Pink → Orange → Yellow → White gradient - Subtle noise added for organic, biological feel **Starting Parameters:** - F = 0.055, k = 0.062 (the classic "coral" pattern configuration) - Du = 0.16, Dv = 0.08 **Pattern Discovery:** - Try different parameter combinations - small changes create vastly different patterns (mitosis, coral, galactic, moving spots, etc.) - Existing patterns can be mutated by adding new seeds The simulation runs entirely in your browser with no external dependencies!