fdars (version 0.3.3)

detect.seasonality.changes: Detect Changes in Seasonality

Description

Detects points in time where seasonality starts (onset) or stops (cessation) by monitoring time-varying seasonal strength.

Usage

detect.seasonality.changes(
  fdataobj,
  period,
  threshold = 0.3,
  window_size = NULL,
  min_duration = NULL
)

Value

A list with components:

change_points

Data frame with columns: time, type ("onset" or "cessation"), strength_before, strength_after

strength_curve

Time-varying seasonal strength used for detection

Arguments

fdataobj

An fdata object.

period

Known or estimated period.

threshold

Seasonal strength threshold for classification (0-1). Above threshold = seasonal, below = non-seasonal. Default: 0.3.

window_size

Width of sliding window for strength estimation. Default: 2 * period.

min_duration

Minimum duration to confirm a change. Prevents detection of spurious short-term fluctuations. Default: period.

Examples

# Signal that starts non-seasonal, becomes seasonal, then stops
t <- seq(0, 30, length.out = 600)
X <- ifelse(t < 10, rnorm(sum(t < 10), sd = 0.3),
            ifelse(t < 20, sin(2 * pi * t[t >= 10 & t < 20] / 2),
                   rnorm(sum(t >= 20), sd = 0.3)))
X <- matrix(X, nrow = 1)
fd <- fdata(X, argvals = t)

# Detect changes
changes <- detect.seasonality.changes(fd, period = 2)
print(changes$change_points)  # Should show onset ~10, cessation ~20