4.7. Practicality — Incremental Dynamic Analysis

imselection.compute_practicality_ida(ida_dict)[source]

Practicality measure from an Incremental Dynamic Analysis result.

Estimated as the OLS slope of log(EDP) on log(IM) along the median IDA curve, mirroring the MCA log-linear regression convention. A higher slope indicates a stronger IM–EDP relationship.

Parameters:

ida_dict (dict) – Output of postprocessor.process_ida_results.

Returns:

  • dict with keys

  • * 'b_slope' — log-log slope (higher is better); NaN if the median – curve has fewer than 2 positive-valued points

  • * 'method' — 'IDA'

Theoretical Background

For IDA, practicality is estimated with the same log-linear convention as for MCA, applied to the median IDA curve: it is the ordinary-least-squares slope \(b\) of \(\ln(\text{EDP})\) on \(\ln(\text{IM})\) along the median curve. A higher slope indicates a stronger IM–EDP relationship. The slope is NaN if the median curve has fewer than two positive-valued points.

Example

from openquake.vmtk.imselection import imselection

ims = imselection()
# ida_dict is the output of postprocessor.process_ida_results()
result = ims.compute_practicality_ida(ida_dict)
print(f"Practicality (slope b) = {result['b_slope']:.4f}")