Description Usage Arguments Value See Also Examples

This `selfStart`

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

attribute that
creates initial estimates of the parameters `Asym`

,
`xmid`

, `scal`

and `lpow`

.

1 | ```
SSRichards(input, Asym, xmid, scal, lpow)
``` |

`input` |
a numeric vector of values at which to evaluate the model. |

`Asym` |
a numeric parameter representing the asymptote. |

`xmid` |
a numeric parameter representing the |

`scal` |
a numeric scale parameter on the |

`lpow` |
the natural logarithm of the inverse of the power to which the denominator is raised. |

a numeric vector of the same length as `input`

. It is the value of
the expression `Asym*(1+exp((xmid-input)/scal))^(-exp(-lpow))`

.
If all of the arguments `Asym`

, `xmid`

, `scal`

and
`lpow`

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

.

1 | ```
summary(fm1 <- nls(Length ~ SSRichards(Time, Asym, xmid, scal, lpow), Leaves))
``` |

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