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feat(letsplot): implement bode-basic (#5158)
## Implementation: `bode-basic` - letsplot Implements the **letsplot** version of `bode-basic`. **File:** `plots/bode-basic/implementations/letsplot.py` **Parent Issue:** #4411 --- :robot: *[impl-generate workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/23388395540)* --------- 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>
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‎plots/bode-basic/implementations/letsplot.py‎

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""" pyplots.ai
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bode-basic: Bode Plot for Frequency Response
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Library: letsplot 4.9.0 | Python 3.14.3
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Quality: 90/100 | Created: 2026-03-21
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"""
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import numpy as np
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import pandas as pd
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from lets_plot import * # noqa: F403
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from lets_plot.export import ggsave as export_ggsave
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from scipy import signal
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LetsPlot.setup_html() # noqa: F405
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# Data - 3rd-order system: G(s) = 500 / ((s+20)(s^2+2s+25))
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# Complex poles (wn=5, zeta=0.2) give a prominent resonance peak ~8 dB
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# Real pole at s=-20 preserves resonance shape
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# Stable system with GM≈5 dB and PM≈18°
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num = [500.0]
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den = np.polymul([1, 20], [1, 2.0, 25])
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system = signal.TransferFunction(num, den)
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omega = np.logspace(-1, 2.5, 500)
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_, mag, phase_deg = signal.bode(system, omega)
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frequency_hz = omega / (2 * np.pi)
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# Build DataFrames
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df_mag = pd.DataFrame({"frequency_hz": frequency_hz, "magnitude_db": mag})
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df_phase = pd.DataFrame({"frequency_hz": frequency_hz, "phase_deg": phase_deg})
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# Gain crossover frequency (where magnitude crosses 0 dB)
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zero_crossings = np.where(np.diff(np.sign(mag)))[0]
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if len(zero_crossings) > 0:
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idx_gc = zero_crossings[0]
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t = abs(mag[idx_gc]) / (abs(mag[idx_gc]) + abs(mag[idx_gc + 1]))
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freq_gc = frequency_hz[idx_gc] + t * (frequency_hz[idx_gc + 1] - frequency_hz[idx_gc])
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phase_at_gc = phase_deg[idx_gc] + t * (phase_deg[idx_gc + 1] - phase_deg[idx_gc])
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phase_margin = 180 + phase_at_gc
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else:
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freq_gc = None
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phase_margin = None
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# Phase crossover frequency (where phase crosses -180 deg)
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phase_crossings = np.where(np.diff(np.sign(phase_deg + 180)))[0]
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if len(phase_crossings) > 0:
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idx_pc = phase_crossings[0]
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t_pc = abs(phase_deg[idx_pc] + 180) / (abs(phase_deg[idx_pc] + 180) + abs(phase_deg[idx_pc + 1] + 180))
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freq_pc = frequency_hz[idx_pc] + t_pc * (frequency_hz[idx_pc + 1] - frequency_hz[idx_pc])
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mag_at_pc = mag[idx_pc] + t_pc * (mag[idx_pc + 1] - mag[idx_pc])
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gain_margin = -mag_at_pc
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else:
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freq_pc = None
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gain_margin = None
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# Colors - colorblind-safe palette (no red-green)
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COLOR_MAIN = "#1B4F72"
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COLOR_REF = "#AEB6BF"
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COLOR_GM = "#D35400" # Orange for gain margin
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COLOR_PM = "#2471A3" # Blue for phase margin
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# Common theme
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common_theme = flavor_high_contrast_light() + theme( # noqa: F405
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axis_text=element_text(size=16), # noqa: F405
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axis_title=element_text(size=20, face="bold"), # noqa: F405
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panel_grid_major=element_line(color="#E0E0E0", size=0.3), # noqa: F405
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panel_grid_minor=element_blank(), # noqa: F405
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panel_border=element_blank(), # noqa: F405
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axis_line=element_line(color="#AAAAAA", size=0.5), # noqa: F405
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plot_margin=[30, 30, 10, 20],
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)
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# Magnitude plot
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mag_plot = (
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ggplot(df_mag, aes(x="frequency_hz", y="magnitude_db")) # noqa: F405
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+ geom_line( # noqa: F405
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color=COLOR_MAIN,
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size=2.5,
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tooltips=layer_tooltips() # noqa: F405
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.format("frequency_hz", ".3f")
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.format("magnitude_db", ".1f")
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.line("Freq: @frequency_hz Hz")
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.line("Mag: @magnitude_db dB"),
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)
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+ geom_hline(yintercept=0, color=COLOR_REF, size=0.8, linetype="dashed") # noqa: F405
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+ scale_x_log10() # noqa: F405
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+ scale_y_continuous(limits=[-35, max(mag) + 3]) # noqa: F405
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+ labs( # noqa: F405
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x="", y="Magnitude (dB)", title="bode-basic \u00b7 letsplot \u00b7 pyplots.ai"
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)
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+ theme(plot_title=element_text(size=26, hjust=0.5, face="bold")) # noqa: F405
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+ common_theme
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+ ggsize(1600, 450) # noqa: F405
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)
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# Add gain margin annotation if phase crossover exists
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if freq_pc is not None:
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gm_seg = pd.DataFrame({"x": [freq_pc], "y": [mag_at_pc], "xend": [freq_pc], "yend": [0.0]})
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gm_pts = pd.DataFrame({"x": [freq_pc, freq_pc], "y": [0.0, mag_at_pc]})
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gm_label = pd.DataFrame({"x": [freq_pc * 3.0], "y": [mag_at_pc - 5], "label": [f"GM = {gain_margin:.1f} dB"]})
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mag_plot = (
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mag_plot
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+ geom_vline(xintercept=freq_pc, color=COLOR_GM, size=0.5, linetype="dotted", alpha=0.5) # noqa: F405
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+ geom_segment( # noqa: F405
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aes(x="x", y="y", xend="xend", yend="yend"), # noqa: F405
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data=gm_seg,
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color=COLOR_GM,
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size=3.0,
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arrow=arrow(type="closed", length=8, ends="both"), # noqa: F405
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)
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+ geom_point( # noqa: F405
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aes(x="x", y="y"), # noqa: F405
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data=gm_pts,
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color=COLOR_GM,
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size=10,
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shape=18,
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)
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+ geom_label( # noqa: F405
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aes(x="x", y="y", label="label"), # noqa: F405
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data=gm_label,
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size=18,
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color=COLOR_GM,
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fill="#FDEBD0",
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label_padding=0.3,
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label_r=0.15,
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fontface="bold",
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)
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)
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# Add gain crossover point on magnitude plot
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if freq_gc is not None:
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gc_mag_pt = pd.DataFrame({"x": [freq_gc], "y": [0.0]})
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mag_plot = mag_plot + geom_point( # noqa: F405
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aes(x="x", y="y"), # noqa: F405
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data=gc_mag_pt,
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color=COLOR_PM,
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size=10,
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shape=18,
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)
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# Phase plot
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phase_plot = (
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ggplot(df_phase, aes(x="frequency_hz", y="phase_deg")) # noqa: F405
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+ geom_line( # noqa: F405
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color=COLOR_MAIN,
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size=2.5,
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tooltips=layer_tooltips() # noqa: F405
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.format("frequency_hz", ".3f")
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.format("phase_deg", ".1f")
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.line("Freq: @frequency_hz Hz")
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.line("Phase: @phase_deg\u00b0"),
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)
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+ geom_hline(yintercept=-180, color=COLOR_REF, size=0.8, linetype="dashed") # noqa: F405
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+ scale_x_log10() # noqa: F405
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+ labs(x="Frequency (Hz)", y="Phase (\u00b0)") # noqa: F405
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+ common_theme
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+ ggsize(1600, 450) # noqa: F405
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)
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# Add phase margin annotation if gain crossover exists
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if freq_gc is not None:
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pm_seg = pd.DataFrame({"x": [freq_gc], "y": [phase_at_gc], "xend": [freq_gc], "yend": [-180.0]})
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pm_pts = pd.DataFrame({"x": [freq_gc, freq_gc], "y": [-180.0, phase_at_gc]})
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pm_label = pd.DataFrame(
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{"x": [freq_gc * 2.5], "y": [phase_at_gc + 10], "label": [f"PM = {phase_margin:.1f}\u00b0"]}
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)
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phase_plot = (
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phase_plot
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+ geom_vline(xintercept=freq_gc, color=COLOR_PM, size=0.5, linetype="dotted", alpha=0.5) # noqa: F405
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+ geom_segment( # noqa: F405
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aes(x="x", y="y", xend="xend", yend="yend"), # noqa: F405
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data=pm_seg,
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color=COLOR_PM,
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size=3.0,
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arrow=arrow(type="closed", length=8, ends="both"), # noqa: F405
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)
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+ geom_point( # noqa: F405
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aes(x="x", y="y"), # noqa: F405
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data=pm_pts,
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color=COLOR_PM,
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size=10,
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shape=18,
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)
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+ geom_label( # noqa: F405
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aes(x="x", y="y", label="label"), # noqa: F405
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data=pm_label,
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size=18,
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color=COLOR_PM,
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fill="#D4E6F1",
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label_padding=0.3,
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label_r=0.15,
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fontface="bold",
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)
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)
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# Add phase crossover point on phase plot
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if freq_pc is not None:
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pc_phase_pt = pd.DataFrame({"x": [freq_pc], "y": [-180.0]})
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phase_plot = phase_plot + geom_point( # noqa: F405
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aes(x="x", y="y"), # noqa: F405
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data=pc_phase_pt,
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color=COLOR_GM,
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size=10,
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shape=18,
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)
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# Combine vertically
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combined = ggbunch( # noqa: F405
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plots=[mag_plot, phase_plot], regions=[(0, 0, 1, 0.53, 0, 0), (0, 0.47, 1, 0.55, 0, 0)]
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)
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# Save
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export_ggsave(combined, filename="plot.png", path=".", scale=3)
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export_ggsave(combined, filename="plot.html", path=".")

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