EVOLUTION-MANAGER
Edit File: SSweibull.html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><title>R: Self-Starting Nls Weibull Growth Curve Model</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <link rel="stylesheet" type="text/css" href="R.css" /> </head><body> <table width="100%" summary="page for SSweibull {stats}"><tr><td>SSweibull {stats}</td><td style="text-align: right;">R Documentation</td></tr></table> <h2>Self-Starting Nls Weibull Growth Curve Model</h2> <h3>Description</h3> <p>This <code>selfStart</code> model evaluates the Weibull model for growth curve data and its gradient. It has an <code>initial</code> attribute that will evaluate initial estimates of the parameters <code>Asym</code>, <code>Drop</code>, <code>lrc</code>, and <code>pwr</code> for a given set of data. </p> <h3>Usage</h3> <pre> SSweibull(x, Asym, Drop, lrc, pwr) </pre> <h3>Arguments</h3> <table summary="R argblock"> <tr valign="top"><td><code>x</code></td> <td> <p>a numeric vector of values at which to evaluate the model.</p> </td></tr> <tr valign="top"><td><code>Asym</code></td> <td> <p>a numeric parameter representing the horizontal asymptote on the right side (very small values of <code>x</code>).</p> </td></tr> <tr valign="top"><td><code>Drop</code></td> <td> <p>a numeric parameter representing the change from <code>Asym</code> to the <code>y</code> intercept.</p> </td></tr> <tr valign="top"><td><code>lrc</code></td> <td> <p>a numeric parameter representing the natural logarithm of the rate constant.</p> </td></tr> <tr valign="top"><td><code>pwr</code></td> <td> <p>a numeric parameter representing the power to which <code>x</code> is raised.</p> </td></tr> </table> <h3>Details</h3> <p>This model is a generalization of the <code><a href="SSasymp.html">SSasymp</a></code> model in that it reduces to <code>SSasymp</code> when <code>pwr</code> is unity. </p> <h3>Value</h3> <p>a numeric vector of the same length as <code>x</code>. It is the value of the expression <code>Asym-Drop*exp(-exp(lrc)*x^pwr)</code>. If all of the arguments <code>Asym</code>, <code>Drop</code>, <code>lrc</code>, and <code>pwr</code> are names of objects, the gradient matrix with respect to these names is attached as an attribute named <code>gradient</code>. </p> <h3>Author(s)</h3> <p>Douglas Bates</p> <h3>References</h3> <p>Ratkowsky, David A. (1983), <em>Nonlinear Regression Modeling</em>, Dekker. (section 4.4.5) </p> <h3>See Also</h3> <p><code><a href="nls.html">nls</a></code>, <code><a href="selfStart.html">selfStart</a></code>, <code><a href="SSasymp.html">SSasymp</a></code> </p> <h3>Examples</h3> <pre> Chick.6 <- subset(ChickWeight, (Chick == 6) & (Time > 0)) SSweibull(Chick.6$Time, 160, 115, -5.5, 2.5) # response only local({ Asym <- 160; Drop <- 115; lrc <- -5.5; pwr <- 2.5 SSweibull(Chick.6$Time, Asym, Drop, lrc, pwr) # response _and_ gradient }) getInitial(weight ~ SSweibull(Time, Asym, Drop, lrc, pwr), data = Chick.6) ## Initial values are in fact the converged values fm1 <- nls(weight ~ SSweibull(Time, Asym, Drop, lrc, pwr), data = Chick.6) summary(fm1) ## Data and Fit: plot(weight ~ Time, Chick.6, xlim = c(0, 21), main = "SSweibull() fit to Chick.6") ux <- par("usr")[1:2]; x <- seq(ux[1], ux[2], length.out=250) lines(x, do.call(SSweibull, c(list(x=x), coef(fm1))), col = "red", lwd=2) As <- coef(fm1)[["Asym"]]; abline(v = 0, h = c(As, As - coef(fm1)[["Drop"]]), lty = 3) </pre> <hr /><div style="text-align: center;">[Package <em>stats</em> version 3.6.0 <a href="00Index.html">Index</a>]</div> </body></html>