P7c {Dark} | R Documentation |
Seven parameter model
Description
The seven parameter model. An exponential decay followed by two linear phases.
Usage
P7c(a, X)
Arguments
a |
An array of parameters;
| ||||||||||||||||||||||||||
X |
The times when the model predicts thresholds. |
Details
This function has three roles, to calculate the thresholds for given parameters a
and times X
. If missing X
, then the function calls the values x
and y
from the .Globalenv
and calculates the sum of residuals squared error (SSE) for a
. If a
is an array of length 1L
or boolean
then a description of the model is returned.
The use of the function H
rather than an impulse function gives a three-fold increase is speed for the optim
function.
Value
The output depends upon the input.
If the input is an array of length 1L
or a boolean
then a list is returned
Pn |
number of parameters |
Mod |
name of the model |
If a parameter array is passed then the sum of residuals squared is calculated. This is used by optim
to optimise the parameter estimates.
Passing a parameter array and a series of putative times causes the function to return predicted thresholds.
Author(s)
Jeremiah MF Kelly
Faculty of Life Sciences, The University of Manchester, M13 9PL, UK
References
O. Mahroo and T. Lamb. Recovery of the human photopic electroretinogram after bleaching exposures: estimation of pigment regeneration kinetics. The Journal of Physiology, 554(2):417, 2004.
T. Lamb and E. Pugh. Dark adaptation and the retinoid cycle of vision. Progress in Retinal and Eye Research, 23(3):307-380, 2004.
See Also
Examples
set.seed(1234)
x <- 0:20
a <- c(-1.00, 1.00, 1.00, -0.24, 6.00, 0.20, 13.00)
tmp <- TestData(x, a)
y <- tmp$resid
# P7c(TRUE)
# Describes the model
# P7c(a)
# The sum of squared residuals
# P7c(a,x)
# The fitted thresholds for given parameters 'a' and times 'x'