Quiver Plots

Compare radial, circular, and spiral vector fields with clear arrow scaling and color magnitude.

import matplotlib.pyplot as plt
import numpy as np

import dartwork_mpl as dm

# Apply scientific style preset
# Default: font.size=7.5, lines.linewidth=0.5, axes.linewidth=0.3
dm.style.use("scientific")

# Generate vector field data
x = np.linspace(-3, 3, 15)
y = np.linspace(-3, 3, 15)
X, Y = np.meshgrid(x, y)

# Vector field: circular flow
U = -Y
V = X

# Vector field: radial flow
U2 = X
V2 = Y

# Vector field: spiral flow
U3 = -Y + 0.3 * X
V3 = X + 0.3 * Y

# Create figure (square-ish): 16 cm wide, 12 cm tall
fig = plt.figure(figsize=(dm.cm2in(16), dm.cm2in(12)), dpi=300)

# Create GridSpec for 4 subplots (2x2)
gs = fig.add_gridspec(
    nrows=2,
    ncols=2,
    left=0.08,
    right=0.98,
    top=0.92,
    bottom=0.12,
    wspace=0.25,
    hspace=0.5,
)

# Panel A: Basic quiver plot
ax1 = fig.add_subplot(gs[0, 0])
# Explicit parameters: scale=5, width=0.003, color
ax1.quiver(
    X,
    Y,
    U,
    V,
    color="oc.blue5",
    scale=5,
    width=0.003,
    angles="xy",
    scale_units="xy",
)
ax1.set_xlabel("X", fontsize=dm.fs(0))
ax1.set_ylabel("Y", fontsize=dm.fs(0))
ax1.set_title("Circular Flow", fontsize=dm.fs(1))
ax1.set_aspect("equal")
ax1.set_xticks([-3, -1, 1, 3])
ax1.set_yticks([-3, -1, 1, 3])
ax1.grid(True, linestyle="--", linewidth=0.3, alpha=0.3)

# Panel B: Radial flow
ax2 = fig.add_subplot(gs[0, 1])
# Explicit parameters: scale=8, width=0.003
ax2.quiver(
    X,
    Y,
    U2,
    V2,
    color="oc.red5",
    scale=8,
    width=0.003,
    angles="xy",
    scale_units="xy",
)
ax2.set_xlabel("X", fontsize=dm.fs(0))
ax2.set_ylabel("Y", fontsize=dm.fs(0))
ax2.set_title("Radial Flow", fontsize=dm.fs(1))
ax2.set_aspect("equal")
ax2.set_xticks([-3, -1, 1, 3])
ax2.set_yticks([-3, -1, 1, 3])
ax2.grid(True, linestyle="--", linewidth=0.3, alpha=0.3)

# Panel C: Spiral flow
ax3 = fig.add_subplot(gs[1, 0])
# Explicit parameters: scale=6, width=0.003
ax3.quiver(
    X,
    Y,
    U3,
    V3,
    color="oc.green5",
    scale=6,
    width=0.003,
    angles="xy",
    scale_units="xy",
)
ax3.set_xlabel("X", fontsize=dm.fs(0))
ax3.set_ylabel("Y", fontsize=dm.fs(0))
ax3.set_title("Spiral Flow", fontsize=dm.fs(1))
ax3.set_aspect("equal")
ax3.set_xticks([-3, -1, 1, 3])
ax3.set_yticks([-3, -1, 1, 3])
ax3.grid(True, linestyle="--", linewidth=0.3, alpha=0.3)

# Panel D: Divergence field (sinks/sources)
ax4 = fig.add_subplot(gs[1, 1])
U4 = np.cos(X) - Y / 3
V4 = np.sin(Y) - X / 3
ax4.quiver(
    X,
    Y,
    U4,
    V4,
    color="oc.purple5",
    scale=8,
    width=0.003,
    angles="xy",
    scale_units="xy",
)
ax4.set_xlabel("X", fontsize=dm.fs(0))
ax4.set_ylabel("Y", fontsize=dm.fs(0))
ax4.set_title("Divergence Patterns", fontsize=dm.fs(1))
ax4.set_aspect("equal")
ax4.set_xticks([-3, -1, 1, 3])
ax4.set_yticks([-3, -1, 1, 3])
ax4.grid(True, linestyle="--", linewidth=0.3, alpha=0.3)

# Optimize layout
dm.simple_layout(fig, gs=gs)

# Show plot
plt.show()