sigmoid function

Sigmoid Growth Equation

sigmoid is used to calculate the $y$ values (e.g., biomass, height, body length, and so on) at given investigation times. UTF-8

sigmoid(expr, P, x, simpver = 1, subdivisions = 100L,
        rel.tol = .Machine$double.eps^0.25, 
        abs.tol = rel.tol, stop.on.error = TRUE, 
        keep.xy = FALSE, aux = NULL)

Arguments

• expr: a performance equation or one of its simplified versions.
• P: the parameters of the performance equation or one of its simplified versions.
• x: the given investigation times.
• simpver: an optional argument to use the simplfied version of the performance equation.
• subdivisions: please see the arguments for the integrate function in package stats.
• rel.tol: please see the arguments for the integrate function in package stats.
• abs.tol: please see the arguments for the integrate function in package stats.
• stop.on.error: please see the arguments for the integrate function in package stats.
• keep.xy: please see the arguments for the integrate function in package stats.
• aux: please see the arguments for the integrate function in package stats.

Details

The performance equations denote MbetaE, MBriereE, MLRFE, and their simplified versions. The arguments of P and simpver should correspond to expr (i.e., MbetaE, MBriereE, MLRFE, and MPerformanceE). The sigmoid curve is the integral of the performance equation or one of its simplified versions.

Returns

The $y$ values (i.e., biomass, height, body length, and so on) at given investigation times. The growth euqation is actually an integral of the performance equation or one of its simplified versions.

Note

Here, the user can define other performance equations, but new equations or their simplified versions should include the lower and upper thresholds in the $x$-axis corresponding to $y = 0$, whose indices of the parameters in P should be the same as those in MbetaE, MBriereE, MLRFE, and MPerformanceE).

Author(s)

Peijian Shi pjshi@njfu.edu.cn , Johan Gielis johan.gielis@uantwerpen.be , Brady K. Quinn Brady.Quinn@dfo-mpo.gc.ca .

References

Jin, J., Quinn, B.K., Shi, P. (2022) The modified Brière equation and its applications. Plants 11, 1769. tools:::Rd_expr_doi("10.3390/plants11131769")

Lian, M., Shi, P., Zhang, L., Yao, W., Gielis, J., Niklas, K.J. (2023) A generalized performance equation and its application in measuring the Gini index of leaf size inequality. Trees $-$ Structure and Function 37, 1555$-$1565. tools:::Rd_expr_doi("10.1007/s00468-023-02448-8")

Shi, P., Fan, M., Ratkowsky, D.A., Huang, J., Wu, H., Chen, L., Fang, S., Zhang, C. (2017) Comparison of two ontogenetic growth equations for animals and plants. Ecological Modelling 349, 1$-$10. tools:::Rd_expr_doi("10.1016/j.ecolmodel.2017.01.012")

Shi, P., Gielis, J., Quinn, B.K., Niklas, K.J., Ratkowsky, D.A., Schrader, J., Ruan, H., Wang, L., Niinemets, Ü. (2022) 'biogeom': An R package for simulating and fitting natural shapes. Annals of the New York Academy of Sciences 1516, 123$-$134. tools:::Rd_expr_doi("10.1111/nyas.14862")

See Also

fitsigmoid, MbetaE, MBriereE, MLRFE, and MPerformanceE

Examples

Pa1 <- c(3, 3, 10, 1)
xv1 <- seq(-5, 15, len=2000)
yv1 <- sigmoid(MBriereE, P=Pa1, x=xv1, simpver=1)
Pa2 <- c(3, 3, 2, 12, 1)
yv2 <- sigmoid(MBriereE, P=Pa2, x=xv1, simpver=NULL)
Pa3 <- c(200, 1.32, 0.85, 12, 3.7, 17)
yv3 <- sigmoid(MPerformanceE, P=Pa3, x=xv1, simpver=1)

dev.new()
plot( xv1, yv2, cex.lab=1.5, cex.axis=1.5, type="l", col=4,
      xlab=expression(italic(x)), ylab=expression(italic(y)) )
lines( xv1, yv1, col=2 )
lines( xv1, yv3, col=3 )

graphics.off()