Animation

econ-viz v1.4.0 adds a lightweight GIF workflow built around Animator. The API stays close to normal plotting: you write a frame factory that returns a fresh Canvas or Figure, then sweep a numeric frame sequence and save the result as a GIF.

Install

pip install "econ-viz[animation]"

If you also want notebook widgets, install:

pip install "econ-viz[all]"

Minimal example

import numpy as np

from econ_viz import Canvas, levels, solve
from econ_viz.animation import Animator
from econ_viz.models import CobbDouglas

def draw(px: float) -> Canvas:
    model = CobbDouglas(alpha=0.5, beta=0.5)
    eq = solve(model, px=px, py=2.0, income=20.0)
    lvls = levels.around(eq.utility, n=5)

    return (
        Canvas(x_max=14, y_max=12, x_label="X_1", y_label="X_2", title="Price sweep")
        .add_utility(model, levels=lvls)
        .add_budget(px=px, py=2.0, income=20.0, fill=True)
        .add_equilibrium(eq, show_ray=True, drop_dashes=True)
    )

Animator(draw, frames=np.linspace(1.0, 6.0, 45)).save(
    "price_sweep.gif",
    fps=12,
    dpi=120,
)

Teaching sweeps

The local example script at examples/animation.py now generates three separate sweep families:

• Parameter sweeps: move one utility-function parameter while holding prices and income fixed.
• Price sweeps: hold the utility function fixed and sweep p_x while holding p_y fixed.
• Income sweeps: hold the utility function and prices fixed and move only income.
• Budget-only sweeps: remove the utility layer entirely so students can isolate budget-line motion.

The docs site embeds the same GIF assets directly, so what you see here matches the locally generated examples.

Parameter sweeps

These animations answer “how does the preference map itself change?”

Cobb-Douglas: vary alpha while beta = 1 - alpha.

CES: vary rho to change curvature and substitutability.

Perfect substitutes: vary a with b fixed.

Leontief: vary a with b fixed to move the kink path.

Price sweeps

These animations answer “how does equilibrium move when the budget line rotates?” The key design choice in v1.4.0 is that the utility function is held fixed, and the background indifference-map levels are also held fixed.

Cobb-Douglas price sweep with p_y fixed.

CES price sweep with a fixed utility surface.

Perfect substitutes under a rotating budget line.

Leontief price sweep with fixed right-angle indifference curves.

Budget-only price sweep for isolating pure rotation of the constraint.

Income sweeps

These animations answer “how does equilibrium move when the budget line shifts in parallel?”

Cobb-Douglas income sweep with fixed prices.

CES income sweep with fixed prices and fixed utility function.

Perfect substitutes income sweep.

Leontief income sweep with fixed prices.

Budget-only income sweep for isolating parallel shifts in the constraint.

Export notes

• Animator.save() uses Pillow, so no ffmpeg dependency is required.
• GIF frames are composited onto white before export to prevent frame stacking artifacts.
• fps, dpi, and loop are configurable per animation.

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