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RMS, minimum, and maximum

Response measures reduce the displacement history retained by a frequency sweep to values that can be compared across initial conditions and frequency. Pass one to TimeIntegration(response_measure=...).

Choose the measure for the question

  • Demodulation is the usual choice for harmonic amplitude and phase at one or more drive-frequency multiples.
  • RMS reports root-mean-square displacement. It is useful when phase is not meaningful or when a broadband scalar level is sufficient.
  • Min and Max report the extrema across the retained time samples.

All measures produce modal values and a total value. The total is formed from the modal displacement using modal_contributions; omit it to use unit weights for every mode.

measure = poscidyn.RMS(modal_contributions=jnp.array([1.0, 0.25]))
solver = poscidyn.TimeIntegration(
    oscillator=oscillator,
    excitation=excitation,
    response_measure=measure,
    n_time_steps=128,
)

RMS, Min, and Max do not estimate a phase. Their results are still available through result.forward.modal.amplitude and result.forward.total.amplitude so that plotting code can remain consistent.

For phase-resolved periodic responses, use Demodulation.