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Double pendulum · gpt-5.4-nano

Simulate a chaotic double pendulum on a canvas using the correct equations of motion, drawing the arms and a colorful fading trail of the tip.

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user

Simulate a chaotic double pendulum on a canvas using the correct equations of motion, drawing the arms and a colorful fading trail of the tip.

assistant
thinking
**Considering implementation details**

I'm looking at how to implement this with angles from vertical downward. The equations I found match many resources. Adding controls for pause or reset could be helpful, but I want to keep it minimal. 

I need to draw arms with specified joint positions, and I plan to scale pixels effectively. The colorful fading trail is interesting; I’ll maintain a history array for positions and their age, possibly limiting the length to avoid performance issues while maintaining visual quality.**Exploring color implementation**

I’m thinking about how to compute hue for colors based on age, like using an equation that factors in time and index. Clearing with transparent black will help retain older pixels and create a fading effect, but the colors might become static. 

Instead, I could store hue history at insertion and redraw each frame after clearing. I like the idea of updating segments with different colors without fully re-rendering the history. For fading, I’ll use a translucent black overlay each frame while keeping the background dark.**Planning the implementation**

I’m considering how to structure the drawing process: I should clear the canvas at the start and then fill it with a fading black overlay every frame. After that, I’ll draw the trail from the previous tip position to the current one, using HSL for color. 

I’ll also add distinct arm colors and maybe some small circles for masses. To create a chaotic feel, I’ll use slightly different initial angles and random elements. It might be useful to include keyboard controls for resetting and pausing. I’m thinking of integrating a stable RK4 method with adaptive time steps.**Setting up frame calculations**

For each frame, I need to calculate the number of steps based on the time elapsed, capping it at a maximum of 10 for stability. I’ll use an accumulator to keep track of the accumulated time. It’s also important to keep track of the previous tip position, and for the first point, I’ll just store its position. 

Next, I should implement a function that calculates derivatives for the equations. Finally, I have to set up the `index.html` in the workspace, which I'll write using my tools.
write index.html (10232 bytes)
toolResult

Successfully wrote 10232 bytes to index.html

assistant

Created **`index.html`** (single self-contained file) that simulates a **chaotic double pendulum** on a canvas using the **standard correct coupled equations of motion** (angles from vertical downward, integrated with **RK4**). It draws both arms and a **colorful fading trail** of the tip. You can run it by opening `index.html` in your browser.

TAKE IT TO CODE

A single self-contained HTML file — copy it and open in any browser, or reuse the prompt with your own pi-agent run.

RUN

modelgpt-5.4-nano
vendorOpenAI
harnesspi-agent
generated2026-07-22

EVALUATION

4/5 working

Double pendulum with fading colorful trail animates chaotically; click/drag/wheel/enter+space reset or perturb it, arrows/wasd have no effect.

Vision grade · anthropic/claude-sonnet-5

MEASUREMENTS

Raw readings from the capture, not a verdict — the grade above is the only judgement. Percentages are how much of the screen changed; the measure under-reports sparse motion on a dark background.

idle motion3.3%
on click6.2%
on drag6.7%
on wheel8.4%
on enter + space5.4%
on arrow keys0.0%
on w/a/s/d0.0%
frame spread11.6 / 255
console errors0
js errors none

METRICS

runtime46.6s
tokens in5.9k
tokens out4.7k
cached0
cost / run$0.0071