# SSgompertz

##### Self-Starting Nls Gompertz Growth Model

This `selfStart`

model evaluates the Gompertz growth model
and its gradient. It has an `initial`

attribute that
creates initial estimates of the parameters `Asym`

,
`b2`

, and `b3`

.

- Keywords
- models

##### Usage

`SSgompertz(x, Asym, b2, b3)`

##### Arguments

- x
- a numeric vector of values at which to evaluate the model.
- Asym
- a numeric parameter representing the asymptote.
- b2
- a numeric parameter related to the value of the function at
`x = 0`

- b3
- a numeric parameter related to the scale the
`x`

axis.

##### Value

a numeric vector of the same length as `input`

. It is the value of
the expression `Asym*exp(-b2*b3^x)`

. If all of
the arguments `Asym`

, `b2`

, and `b3`

are
names of objects the gradient matrix with respect to these names is attached as
an attribute named `gradient`

.

##### See Also

##### Examples

`library(stats)`

```
DNase.1 <- subset(DNase, Run == 1)
SSgompertz(log(DNase.1$conc), 4.5, 2.3, 0.7) # response only
Asym <- 4.5; b2 <- 2.3; b3 <- 0.7
SSgompertz(log(DNase.1$conc), Asym, b2, b3) # response and gradient
print(getInitial(density ~ SSgompertz(log(conc), Asym, b2, b3),
data = DNase.1), digits = 5)
## Initial values are in fact the converged values
fm1 <- nls(density ~ SSgompertz(log(conc), Asym, b2, b3),
data = DNase.1)
summary(fm1)
```

*Documentation reproduced from package stats, version 3.3.3, License: Part of R 3.3.3*

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