Skip to contents

Computes the body wavelength based on the phase at each point and the arc length

Source: R/wavelength.R
get_wavelength.Rd

Computes the spatial derivative in phase relative to arc length using several different possible methods:

  • 'deriv' Computes the derivative directly using deriv()

  • 'slope' Fits a line to the phase relative to arc length and uses the slope of that line as an estimate of the wavelength

  • 'cycle' Looks for pairs of points along the body where the phase differs by a full cycle. The arc length between those points is one wavelength.

  • 'halfcycle' Looks for pairs of points along the body where the phase differs by one half cycle. The arc length between those points is half of a wavelength.

Usage

get_wavelength(
  arclen,
  ph,
  unwrap = TRUE,
  method = "deriv",
  ignore_arclen_vals = NULL,
  sort_arclen = FALSE,
  check_reasonableness = TRUE,
  mod = 2 * pi,
  traveling_wave_dir = -1
)

Arguments

arclen

Arc length

ph

Phase

unwrap

(TRUE or FALSE) Unwrap the phase along the body

method

('deriv', 'slope', 'cycle', 'halfcycle') as explained above

ignore_arclen_vals

NULL or a function that returns TRUE or FALSE for certain values of arclength where the phase estimate is not reliable. This is often used to exclude points near the head (e.g., ignore_arclen_vals = \(s) s < 0.3)

sort_arclen

(TRUE or FALSE) Sort the phase values by arc length before computing the wavelength. Useful if arc lengths arrive out of order. (default = FALSE)

check_reasonableness

(TRUE or FALSE) Check that the phase decreases along the body as expected for a head-to-tail traveling wave, and warn if it does not. (default = TRUE)

mod

Modulus for the phase variable

traveling_wave_dir

(1 or -1) Defines the direction of the traveling wave. For a normal head-to-tail traveling wave, use -1 (default)

Value

The wavelength as a vector the same size as the phase variable

Examples

s <- seq(0, 1, by=0.1)
# artificial data with a wavelength of exactly 0.6
ph <- 2*pi*((1 - s) / 0.6)

get_wavelength(s, ph, ignore_arclen_vals = \(s) s < 0.3)
#>  [1]  NA  NA  NA 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6