feat(plotnine): implement campbell-basic (#4245)

## Implementation: `campbell-basic` - plotnine

Implements the **plotnine** version of `campbell-basic`.

**File:** `plots/campbell-basic/implementations/plotnine.py`

**Parent Issue:** #4241

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/22043026955)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/campbell-basic/implementations/plotnine.py

@@ -0,0 +1,227 @@
+""" pyplots.ai
+campbell-basic: Campbell Diagram
+Library: plotnine 0.15.3 | Python 3.14.3
+Quality: 90/100 | Created: 2026-02-15
+"""
+
+import numpy as np
+import pandas as pd
+from plotnine import (
+    aes,
+    annotate,
+    coord_cartesian,
+    element_blank,
+    element_line,
+    element_rect,
+    element_text,
+    geom_line,
+    geom_point,
+    geom_rect,
+    geom_text,
+    ggplot,
+    guide_legend,
+    guides,
+    labs,
+    scale_color_manual,
+    scale_linetype_manual,
+    scale_size_identity,
+    scale_x_continuous,
+    scale_y_continuous,
+    theme,
+    theme_minimal,
+)
+
+
+# Data — Natural frequencies vs rotational speed for rotating machinery
+np.random.seed(42)
+speed = np.linspace(0, 6000, 80)
+
+# Natural frequency modes with pronounced gyroscopic speed dependence
+modes = {
+    "1st Bending": 18 + speed * 0.0015 + np.random.normal(0, 0.12, len(speed)),
+    "2nd Bending": 45 - speed * 0.002 + np.random.normal(0, 0.12, len(speed)),
+    "1st Torsional": 52 + speed * 0.0025 + np.random.normal(0, 0.12, len(speed)),
+    "2nd Torsional": 75 + speed * 0.001 + np.random.normal(0, 0.12, len(speed)),
+    "Axial": 90 - speed * 0.0004 + np.random.normal(0, 0.12, len(speed)),
+}
+
+# Colorblind-safe palette starting with Python Blue
+palette = ["#306998", "#E69F00", "#882D9E", "#D55E00", "#009E73"]
+mode_names = list(modes.keys())
+mode_colors = dict(zip(mode_names, palette, strict=True))
+eo_color = "#888888"
+
+# Long-format DataFrame for natural frequency curves
+df_modes = pd.DataFrame(
+    [
+        {"Speed": s, "Frequency": f, "Mode": name}
+        for name, freqs in modes.items()
+        for s, f in zip(speed, freqs, strict=True)
+    ]
+)
+
+# Engine order lines: frequency = order × speed / 60
+engine_orders = [1, 2, 3]
+eo_names = [f"{o}x EO" for o in engine_orders]
+df_eo = pd.DataFrame(
+    [{"Speed": s, "Frequency": order * s / 60, "Mode": f"{order}x EO"} for order in engine_orders for s in speed]
+)
+
+# Critical speed intersections (EO line crosses natural frequency curve)
+critical_points = []
+for order in engine_orders:
+    eo_freq = order * speed / 60
+    for _mode_name, freq_values in modes.items():
+        diff = eo_freq - freq_values
+        sign_changes = np.where(np.diff(np.sign(diff)))[0]
+        for idx in sign_changes:
+            s0, s1 = speed[idx], speed[idx + 1]
+            f0_eo, f1_eo = eo_freq[idx], eo_freq[idx + 1]
+            f0_m, f1_m = freq_values[idx], freq_values[idx + 1]
+            t = (f0_m - f0_eo) / ((f1_eo - f0_eo) - (f1_m - f0_m))
+            cs, cf = s0 + t * (s1 - s0), f0_eo + t * (f1_eo - f0_eo)
+            if 0 < cs < 6000 and 0 < cf < 110:
+                critical_points.append({"Speed": cs, "Frequency": cf})
+df_critical = pd.DataFrame(critical_points)
+
+# Storytelling: 1x / 1st Bending critical speed (most operationally significant)
+eo1_freq = speed / 60
+diff_1b = eo1_freq - modes["1st Bending"]
+sc_idx = np.where(np.diff(np.sign(diff_1b)))[0]
+annot_speed = annot_freq = None
+if len(sc_idx) > 0:
+    idx = sc_idx[0]
+    t = (modes["1st Bending"][idx] - eo1_freq[idx]) / (
+        (eo1_freq[idx + 1] - eo1_freq[idx]) - (modes["1st Bending"][idx + 1] - modes["1st Bending"][idx])
+    )
+    annot_speed = speed[idx] + t * (speed[idx + 1] - speed[idx])
+    annot_freq = eo1_freq[idx] + t * (eo1_freq[idx + 1] - eo1_freq[idx])
+
+# Combine all line data and add line weight column for size differentiation
+df_lines = pd.concat([df_modes, df_eo], ignore_index=True)
+df_lines["_lw"] = df_lines["Mode"].apply(lambda m: 2.0 if "EO" not in m else 1.0)
+
+# Legend mappings — consolidated EO into one entry
+color_map = {**mode_colors, **dict.fromkeys(eo_names, eo_color)}
+ltype_map = {**dict.fromkeys(mode_names, "solid"), **dict.fromkeys(eo_names, "dashed")}
+breaks = mode_names + eo_names[:1]
+labels = mode_names + ["Engine Order (1×, 2×, 3×)"]
+
+# Operating range band (nominal: 2000–4500 RPM)
+df_band = pd.DataFrame([{"xmin": 2000, "xmax": 4500, "ymin": 0, "ymax": 110}])
+
+# EO labels positioned along lines
+eo_labels = pd.DataFrame(
+    [
+        {"Speed": 4500, "Frequency": 4500 / 60 + 3, "label": "1×"},
+        {"Speed": 2200, "Frequency": 2 * 2200 / 60 + 3, "label": "2×"},
+        {"Speed": 1500, "Frequency": 3 * 1500 / 60 + 3, "label": "3×"},
+    ]
+)
+
+# Plot — grammar of graphics layer composition
+plot = (
+    ggplot(df_lines, aes("Speed", "Frequency", color="Mode", linetype="Mode", group="Mode"))
+    # Operating range shading
+    + geom_rect(
+        df_band,
+        aes(xmin="xmin", xmax="xmax", ymin="ymin", ymax="ymax"),
+        fill="#306998",
+        alpha=0.04,
+        color="none",
+        inherit_aes=False,
+    )
+    # Natural frequency + EO lines with size-identity for weight differentiation
+    + geom_line(aes(size="_lw"))
+    + scale_size_identity()
+    # Critical speed markers
+    + geom_point(
+        df_critical,
+        aes("Speed", "Frequency"),
+        color="#C62828",
+        fill="#EF5350",
+        size=4.5,
+        shape="D",
+        stroke=0.7,
+        inherit_aes=False,
+        show_legend=False,
+    )
+    # EO line labels
+    + geom_text(
+        eo_labels,
+        aes("Speed", "Frequency", label="label"),
+        color="#555555",
+        size=11,
+        fontstyle="italic",
+        fontweight="bold",
+        inherit_aes=False,
+        show_legend=False,
+    )
+    # Unified legend via scale_manual with custom breaks/labels
+    + scale_color_manual(values=color_map, breaks=breaks, labels=labels)
+    + scale_linetype_manual(values=ltype_map, breaks=breaks, labels=labels)
+    + guides(color=guide_legend(override_aes={"size": [1.8] * 5 + [1.0]}), linetype=guide_legend())
+    # coord_cartesian for zoom without data removal
+    + scale_x_continuous(breaks=range(0, 7000, 1000))
+    + scale_y_continuous(breaks=range(0, 111, 10))
+    + coord_cartesian(xlim=(0, 6200), ylim=(0, 108))
+    + labs(x="Rotational Speed (RPM)", y="Natural Frequency (Hz)", title="campbell-basic · plotnine · pyplots.ai")
+    # Publication-quality theme
+    + theme_minimal(base_size=14)
+    + theme(
+        figure_size=(16, 9),
+        text=element_text(family="sans-serif", color="#333333"),
+        plot_title=element_text(size=24, ha="center", face="bold", color="#1a1a1a"),
+        axis_title_x=element_text(size=20, face="bold", color="#222222"),
+        axis_title_y=element_text(size=20, face="bold", color="#222222"),
+        axis_text=element_text(size=16, color="#555555"),
+        legend_text=element_text(size=13),
+        legend_title=element_blank(),
+        legend_position="bottom",
+        legend_direction="horizontal",
+        legend_background=element_rect(fill="white", alpha=0.9, color="#CCCCCC", size=0.4),
+        legend_key_width=35,
+        legend_key_height=18,
+        panel_grid_major=element_line(color="#E5E5E5", size=0.25),
+        panel_grid_minor=element_blank(),
+        plot_background=element_rect(fill="white", color="white"),
+        panel_background=element_rect(fill="#FAFAFA", color="#E0E0E0", size=0.3),
+        axis_line=element_line(color="#CCCCCC", size=0.4),
+        plot_margin=0.02,
+    )
+)
+
+# Storytelling: annotate the most significant critical speed
+if annot_speed is not None:
+    plot = (
+        plot
+        + annotate(
+            "segment",
+            x=annot_speed,
+            xend=annot_speed,
+            y=0,
+            yend=annot_freq,
+            color="#C62828",
+            linetype="dotted",
+            size=0.7,
+            alpha=0.6,
+        )
+        + annotate(
+            "text",
+            x=annot_speed + 180,
+            y=annot_freq + 5,
+            label=f"Critical: {int(round(annot_speed))} RPM",
+            color="#C62828",
+            size=9,
+            ha="left",
+            fontstyle="italic",
+            fontweight="bold",
+        )
+    )
+
+# Operating range label
+plot = plot + annotate(
+    "text", x=3250, y=104, label="Operating Range", color="#306998", size=8, alpha=0.5, fontweight="bold"
+)
+
+plot.save("plot.png", dpi=300, verbose=False)