All notable changes to CppPlot library will be documented in this file.

• Matrix class for linear algebra operations

  • Addition, subtraction, multiplication
  • Transpose, determinant, inverse
  • Eye, zeros factory methods

• StateSpace class for state-space representation (ẋ = Ax + Bu, y = Cx + Du)

  • Poles calculation via characteristic polynomial
  • Stability check
  • Controllability matrix and test
  • Observability matrix and test

• Conversion Functions:

  • tf2ss(G) - Transfer function to controllable canonical form
  • ss2tf(sys) - State-space to transfer function (SISO)

• Simulation:

  • lsim(sys, u, t, x0) - Arbitrary input simulation
  • ss_step(sys) - Step response of state-space system
  • initial(sys, x0) - Initial condition response

• Pole Placement:

  • acker(A, B, poles) - Ackermann's formula
  • place(A, B, real_poles) - Simplified real pole placement
  • place_complex(A, B, poles) - Complex conjugate poles

• LQR Controller:

  • care(A, B, Q, R) - Continuous algebraic Riccati equation solver
  • lqr(A, B, Q, R) - Linear Quadratic Regulator design
  • lqr_simple(A, B, q_diag, r) - Simplified diagonal weights interface

• Observer Design:

  • observer_gain(A, C, poles) - Luenberger observer via duality
  • place_observer(A, C, poles) - Simplified observer placement

• Sensitivity Analysis:

  • SensitivityFunctions struct (S, T, CS, PS)
  • sensitivity(G, K) - Calculate all sensitivity functions
  • sensitivity_plot(G, K) - Plot sensitivity Bode diagram

• PID Tuning:

  • ziegler_nichols(Ku, Tu, type) - Z-N tuning (P, PI, PID, no-overshoot)
  • cohen_coon(K, T, L, type) - Cohen-Coon for FOPDT plants
  • pid_tf(gains) - Create PID transfer function from gains

• Compensator Design:

  • design_lead(phi_max, wc) - Lead compensator for phase margin
  • design_lag(gain_increase, wc) - Lag compensator for DC gain

• Standard Control Loops:

  • closed_loop(G, C, H) - Standard feedback loop
  • pid_loop(G, Kp, Ki, Kd) - PID control loop
  • two_dof_loop(G, Cr, Cy) - Two degree-of-freedom structure

• Advanced Structures:

  • cascade_control(G1, G2, C1, C2) - Nested/cascade control
  • feedforward_loop(G, C, Cff) - Feedforward compensation
  • nfeedback(G, H) / pfeedback(G, H) - Explicit feedback sign

• Disturbance Analysis:

  • disturbance_to_output(G, C) - d→y transfer function
  • noise_to_output(G, C) - n→y transfer function

• IMC:

  • imc_to_classical(G, Cimc) - Convert IMC to classical form
  • imc_first_order(K, tau, lambda) - IMC design for first-order

• Loop Shaping:

  • gain_for_crossover(G, wc) - Find gain for desired crossover
  • required_phase_lead(G, wc, PM) - Calculate required phase boost

• Added control_design_demo.cpp with comprehensive examples:
  • State-space modeling of DC motor
  • TF ↔ SS conversions
  • Pole placement design
  • LQR controller design
  • Observer design
  • PID tuning methods
  • Lead compensator design
  • Sensitivity function analysis

• nichols(G, options) - Plot Nichols chart for single system
• nichols(systems, labels, options) - Compare multiple systems
• nichols_m_circle(M_dB) - Generate M-circle (constant CL magnitude)
• nichols_n_circle(N_deg) - Generate N-circle (constant CL phase)
• NicholsOptions struct with show_m_circles, show_n_circles, show_margins

• DiscreteTransferFunction class for z-domain transfer functions

  • Sample time handling (Ts)
  • Poles/zeros in z-plane
  • Stability check (unit circle criterion)
  • DC gain, Nyquist frequency

• Discretization Methods:

  • c2d_tustin(Gc, Ts) - Bilinear (Tustin) transform
  • c2d_zoh(Gc, Ts) - Zero-Order Hold approximation

• Discrete Factory Functions:

  • dtf_integrator(Ts) - Forward Euler integrator
  • dtf_integrator_tustin(Ts) - Tustin integrator
  • dtf_lowpass(tau, Ts) - First-order lowpass filter

• Discrete Plotting:

  • dbode(H) - Discrete Bode diagram (0 to Nyquist)
  • dzpmap(H) - Pole-zero map in z-plane with unit circle
  • dstep(H, n) - Discrete step response (stem plot)
  • dsysinfo(H) - Print discrete system information

• Added control_advanced_demo.cpp with 8 comprehensive examples:
  • Nichols chart single/comparison
  • Discrete Bode, pole-zero, step response
  • Continuous to discrete conversion comparison
  • Second-order discretization
  • Digital lowpass filter design

Complete control systems analysis and plotting library following Python Control / MATLAB standards.

New Files:

• control.hpp - Main control module header
• polynomial.hpp - Polynomial arithmetic class
• transfer_function.hpp - Transfer function class with full arithmetic
• analysis.hpp - Margin, stepinfo, bandwidth, stability analysis
• bode.hpp - Automatic Bode plot generation
• nyquist.hpp - Nyquist diagram with critical point
• pzmap.hpp - Pole-zero map with damping lines
• root_locus.hpp - Root locus plotting
• time_response.hpp - Step, impulse response

Transfer Function Features:

• Create from coefficients: TransferFunction G({1}, {1, 2, 1});
• Create from zeros/poles/gain: zpk({-1}, {-2, -3}, 5.0)
• Factory functions: tf_second_order(), tf_first_order(), tf_integrator()
• Arithmetic: Series (*), Parallel (+), Feedback (feedback())
• Properties: poles(), zeros(), dcgain(), isStable()

Analysis Functions:

• margin(G) - Gain and phase margins
• stepinfo(G) - Rise time, settling time, overshoot
• bandwidth(G) - -3dB bandwidth
• damp(G) - Damping ratio and natural frequency of poles

One-liner Plotting (Python Control style):

bode(G);           // Automatic Bode plot
nyquist(G);        // Nyquist diagram  
pzmap(G);          // Pole-zero map
rlocus(G);         // Root locus
step(G);           // Step response
impulse(G);        // Impulse response

Standard Test Systems:

systems::first_order(K, tau);
systems::second_order(wn, zeta, K);
systems::integrator(K);
systems::type1(K, a);
systems::pid(Kp, Ki, Kd);
systems::lead(z, p, K);
systems::lag(z, p, K);

• Added control_module_demo.cpp with comprehensive examples
• Generated SVG outputs: step, bode, nyquist, pzmap, rlocus

• LaTeXRenderer class in core/latex.hpp for converting LaTeX to Unicode
• Support for Greek letters: \alpha, \beta, \gamma, \Delta, \Theta, etc.
• Support for superscripts: x^2, x^{10}, e^{i\pi} → x², x¹⁰, eⁱπ
• Support for subscripts: x_1, x_{12} → x₁, x₁₂
• Support for math operators: \sum, \int, \prod, \partial, \nabla, \infty
• Support for relations: \leq, \geq, \neq, \approx, \equiv
• Support for arrows: \to, \leftarrow, \Rightarrow, \leftrightarrow
• Support for logic symbols: \forall, \exists, \wedge, \vee
• Support for fractions: \frac{a}{b} → (a/b)
• Support for square root: \sqrt{x} → √(x)

• figtext(x, y, text, opts) - Add text at figure coordinates (0-1 normalized)
  • x=0 is left edge, x=1 is right edge
  • y=0 is bottom, y=1 is top
  • Perfect for adding formulas, titles, or annotations anywhere on the figure
• latex(x, y, expr, opts) - Explicitly render LaTeX expression

• Auto-detection of LaTeX in text (backslash commands, ^, _, $)
• usetex option to force LaTeX rendering
• Math font family default for LaTeX text (STIX Two Math, Cambria Math)

• TextAnnotation struct now includes figureCoords, useLaTeX, useMathML flags
• text() function now automatically parses LaTeX commands
• drawAnnotations() now supports figure coordinates and LaTeX rendering

• Added latex_demo.cpp with 8 comprehensive examples:
  • Greek letters in labels
  • Superscripts and subscripts
  • Gaussian distribution with formula
  • Physics equations (projectile motion)
  • Calculus notation (derivatives, integrals)
  • Math symbols reference chart
  • Euler's formula visualization
  • Statistical formulas

• errorbar(x, y, yerr, opts) - Plot with vertical error bars
• errorbar(x, y, xerr, yerr, opts) - Plot with both X and Y error bars
  • Supports capsize option for error bar cap width
  • Supports standard styling options (color, linewidth, label)

• fill_between(x, y1, y2, opts) - Fill area between two curves
• fill_between(x, y, baseline, opts) - Fill area to a constant baseline
  • Supports alpha for transparency
  • Supports color and label options
  • Useful for confidence intervals, stacked areas

• text(x, y, "label", opts) - Add text annotation at data coordinates
• annotate("text", x, y, textX, textY, opts) - Add annotation with arrow
  • Supports fontsize, fontweight, fontstyle
  • Supports color (or textcolor)
  • Supports alignment: ha (left/center/right), va (top/center/bottom)

• set_xscale("log") / xscale("log") - Set X axis to logarithmic scale
• set_yscale("log") / yscale("log") - Set Y axis to logarithmic scale
• Scale can be "linear" (default) or "log"

• axhline(y, opts) - Add horizontal line across the plot
• axvline(x, opts) - Add vertical line across the plot
  • Supports color, linewidth, linestyle
  • Useful for marking thresholds, means, or key values

• Updated Axes class with new private draw methods
• Added niceLogTicks() utility function for log scale tick generation

• Updated README with new feature examples
• Updated AUDIT_REPORT.md with implementation status
• Added new demo files:
  • advanced_demo.cpp - Comprehensive demo of all new features
  • log_scale_demo.cpp - Log scale specific examples

• Line plots with format strings (matplotlib style)
• Scatter plots with size and color mapping
• Bar charts (vertical)
• Histograms with bin control
• Subplot system with flexible layouts
• GridSpec for advanced layouts
• SVG backend for vector output
• Rich styling system (colors, line styles, markers)
• Font customization (size, weight, style, family)
• Legend support
• Grid lines
• Axis labels and titles

• Header-only library
• C++14 compatible
• Cross-platform (Windows, Linux, macOS)
• Matplotlib-like API
• Julia Plots-inspired layout system