flexit: Return the flexit

In HelpersMG: Tools for Environmental Analyses, Ecotoxicology and Various R Functions

Return the flexit

Description

Return a vector with the probabilities. The flexit equation is published in:
Abreu-Grobois, F.A., Morales-Mérida, B.A., Hart, C.E., Guillon, J.-M., Godfrey, M.H., Navarro, E. & Girondot, M. (2020) Recent advances on the estimation of the thermal reaction norm for sex ratios. PeerJ, 8, e8451.
If dose < P then (1 + (2^K1 - 1) * exp(4 * S1 * (P - x)))^(-1/K1)
If dose > P then 1-((1 + (2^K2 - 1) * exp(4 * S2 * (x - P)))^(-1/K2)
with:

S1 = (2^(K1 - 1) * S * K1)/(2^K1 - 1)

S2 = (2^(K2 - 1) * S * K2)/(2^K2 - 1)

If 2^K1 is too large to be estimated, the approximation S1 = S*K1/2 is used.
Demonstration:

S1 = (2^(K1 - 1) * S * K1)/(2^K1 - 1)

S1 = exp(log((2^(K1 - 1) * S * K1)/(2^K1 - 1)))

S1 = exp(log(2^(K1 - 1)) + log(S * K1) - log(2^K1 - 1))

When K1 is very large, 2^K1 - 1 = 2^K1 then

S1 = exp((K1 - 1) * log(2) + log(S * K1) - K1 * log(2))

S1 = exp((K1 * log(2) - log(2) + log(S * K1) - K1 * log(2))

S1 = exp(log(S * K1)- log(2))

S1 = S * K1 / 2

If 2^K2 is too large to be estimated, the approximation S2 = S*K2/2 is used.
If (1 + (2^K1 - 1) * exp(4 * S1 * (P - x)))^(-1/K1) is not finite, the following approximation is used:

exp((-1/K1)*(K1*log(2)+(4*S1*(P-x))))

If 1-((1 + (2^K2 - 1) * exp(4 * S2 * (x - P)))^(-1/K2) is not finite, the following approximation is used:

1 - exp((-1/K2)*(K2*log(2)+(4*S2*(x - P))))

Usage

flexit(
  x,
  par = NULL,
  P = NULL,
  S = NULL,
  K1 = NULL,
  K2 = NULL,
  Min = 0,
  Max = 1,
  zero = 1e-09,
  error0 = 0,
  error1 = 1
)

Arguments

x	The values at which the flexit model must be calculated
par	The vector with P, S, K1, and K2 values
P	P value
S	S value
K1	K1 value
K2	K2 value
Min	Min value for scaled flexit model
Max	Max value for scaled flexit model
zero	Value to replace zero
error0	Value to return if an error is observed toward 0
error1	Value to return if an error is observed toward 1

Details

Return the flexit value

Value

A vector with the probabilities

Author(s)

Marc Girondot [e-mail]

See Also

Other logit: invlogit(), logit()

Examples

n <- flexit(x=1:100, par=c(P=50, S=0.001, K1=0.01, K2=0.02))
n <- flexit(x=1:100, P=50, S=0.001, K1=0.01, K2=0.02)

1/(1+exp(0.01*4*(50-1:100)))
flexit(1:100, P=50, S=0.01, K1=1, K2=1)

HelpersMG documentation built on April 4, 2025, 4:40 a.m.