simEigenmode

simEigenmode

Runs a Verlet dynamics simulation of the packing in which a single selected eigenmode is excited as the initial displacement, then checks the mode's predicted frequency and attenuation against what the dynamics actually produce. Builds neighbor lists once (periodic x/y), displaces the particles along the selected eigenvector (amplitude = P_target * 0.01), integrates for ~500 box-crossings, and plots probe-particle dx(t), dy(t), a |u(t)| attenuation fit (ln|u| vs t), and the FFT amplitude |ũ(omega)|. Saves the figure to data/junkyard/simEigenmode.png and returns the eigen-frequency ratio omega_eig / omega_max.

Default Syntax

strLoadPath = "path/to/results_2D_iso_N100_P0.1_Seed5_gamma_3.00e-03.mat"
simEigenmode(strLoadPath, scalModeFreq = 0.3)   % scalModeFreq: double, target omega

Loads the results file (packing + eigenvalues/eigenvectors), picks the mode closest to the target frequency, simulates it, and reports how well the eigenvalue prediction matches the dynamics.

Options

Mode selection — exactly one must be non-zero:

• opts.scalModeFreq (double, default 0) — target frequency; the eigenmode whose imaginary part is closest to this value is excited.
• opts.scalModeAtten (double, default 0) — target attenuation; the eigenmode whose real part is closest to this value is excited.

Input format:

• opts.loadPolyData (logical, default false) — true: the file holds the outData struct from processEigenModesDampedPara (eigenVectors, eigenValues, radii, positions, Lx, Ly, pressure, damping, springConstant — cells). false: a pack.m results file with packing, eigenvalues, eigenvectors.

Simulation behavior:

• opts.negDy (logical, default false) — flips the y-DOF rows of the eigenvector before use. Needed for results from the old matSpringDampMass convention ([dx,-dy] ordering); compare with and without to identify which convention a results file uses.
• opts.visSim (logical, default false) — draw per-timestep displacement-vs-position plots during the run.
• opts.fullSpectrum (logical, default false) — store every particle's trajectory (N x Nt matrices) for post-processing.
• opts.flagVarMass (logical, default false) — mass proportional to pi/4 * D^2 instead of unit mass.

Examples

% Excite the mode closest to omega = 0.3 in a pack.m results file
simEigenmode("data/eigenData/results_2D_iso_N100_P0.1_Seed5_gamma_3.00e-03.mat", ...
             scalModeFreq = 0.3);

% Same file, but with the old [dx,-dy] eigenvector convention
simEigenmode("data/eigenData/results_2D_iso_N100_P0.1_Seed5_gamma_1.00e-02.mat", ...
             scalModeFreq = 0.3, negDy = true);

% Select by attenuation (beta) instead of frequency
simEigenmode("data/eigenData/results_2D_iso_N100_P0.1_Seed5_gamma_1.00e-02.mat", ...
             scalModeAtten = -0.05);

% outData file (from processEigenModesDampedPara)
simEigenmode("data/junkyard/2D_eigenData_10by10_P0.100_damp0.010_K100_M1.mat", ...
             scalModeFreq = 0.1, loadPolyData = true);

% Large system, visualize the simulation as it runs
simEigenmode("data/eigenData/results_2D_iso_N16000_P0.1_Seed5_gamma_1.00e-03.mat", ...
             scalModeFreq = 0.02, negDy = true, visSim = true);