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Identify the Inflection Point in a Melatonin Profile

Source: R/seek_inflection.R
get_inflection.Rd

This function determines the inflection point in a melatonin profile by calling seek_inflection(), which performs a grid search over a region of interest (ROI).

Usage

get_inflection(
  profile_data,
  threshold = 2.3,
  posix_roi,
  fit_type = "linear",
  fine_flag = TRUE
)

Arguments

profile_data

A tibble containing melatonin profile data with columns:

  • datetime (POSIXct): The timestamp of each measurement.

  • melatonin (numeric): The melatonin concentration.

  • base (binary): Indicator for the baseline segment.

  • ascending (binary): Indicator for the ascending segment.

  • intermediate (optional, binary): Indicator for an intermediate segment.

threshold

Numeric. The threshold value for constraining the fit (default = 2.3).

posix_roi

A list defining the region of interest (ROI) using POSIXct timestamps:

  • x_start: Start time of the ROI.

  • x_end: End time of the ROI.

  • y_min: Minimum melatonin concentration in the ROI.

  • y_max: Maximum melatonin concentration in the ROI.

fit_type

Character. Specifies the type of fit used:

  • "linear" (default): Uses a linear model.

  • "parabolic": Uses a parabolic model for the ascending segment.

fine_flag

Logical. If TRUE, enables fine-grid refinement in seek_inflection() (default = TRUE).

Value

A list containing:

  • inflection_point: The estimated inflection point (x, y).

  • base_params: Parameters of the base segment fit.

  • ascending_params: Parameters of the ascending segment fit.

  • grid_big: The coarse grid used in the first search.

  • res_big: The residuals corresponding to grid_big.

  • grid_small: The fine grid used in the second search (if fine_flag = TRUE).

  • res_small: The residuals corresponding to grid_small (if fine_flag = TRUE).

Details

  • The ROI is converted from POSIXct format to decimal time using posixct_to_decimal().

  • If the profile_data contains an "intermediate" segment, it is included in the fit.

  • Calls seek_inflection() to identify the best-fit inflection point.

See also

seek_inflection, posixct_to_decimal, fit