EVOLUTION-MANAGER
Edit File: SSasympOff.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 Asymptotic Regression Model with an Offset</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 SSasympOff {stats}"><tr><td>SSasympOff {stats}</td><td style="text-align: right;">R Documentation</td></tr></table> <h2>Self-Starting Nls Asymptotic Regression Model with an Offset</h2> <h3>Description</h3> <p>This <code>selfStart</code> model evaluates an alternative parametrization of the asymptotic regression function and the gradient with respect to those parameters. It has an <code>initial</code> attribute that creates initial estimates of the parameters <code>Asym</code>, <code>lrc</code>, and <code>c0</code>. </p> <h3>Usage</h3> <pre> SSasympOff(input, Asym, lrc, c0) </pre> <h3>Arguments</h3> <table summary="R argblock"> <tr valign="top"><td><code>input</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 large values of <code>input</code>).</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>c0</code></td> <td> <p>a numeric parameter representing the <code>input</code> for which the response is zero.</p> </td></tr> </table> <h3>Value</h3> <p>a numeric vector of the same length as <code>input</code>. It is the value of the expression <code>Asym*(1 - exp(-exp(lrc)*(input - c0)))</code>. If all of the arguments <code>Asym</code>, <code>lrc</code>, and <code>c0</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>José Pinheiro and Douglas Bates</p> <h3>See Also</h3> <p><code><a href="nls.html">nls</a></code>, <code><a href="selfStart.html">selfStart</a></code>; <code>example(SSasympOff)</code> gives graph showing the <code>SSasympOff</code> parametrization. </p> <h3>Examples</h3> <pre> CO2.Qn1 <- CO2[CO2$Plant == "Qn1", ] SSasympOff(CO2.Qn1$conc, 32, -4, 43) # response only local({ Asym <- 32; lrc <- -4; c0 <- 43 SSasympOff(CO2.Qn1$conc, Asym, lrc, c0) # response and gradient }) getInitial(uptake ~ SSasympOff(conc, Asym, lrc, c0), data = CO2.Qn1) ## Initial values are in fact the converged values fm1 <- nls(uptake ~ SSasympOff(conc, Asym, lrc, c0), data = CO2.Qn1) summary(fm1) ## Visualize the SSasympOff() model parametrization : xx <- seq(0.25, 8, by=1/16) yy <- 5 * (1 - exp(-(xx - 3/4)*0.4)) stopifnot( all.equal(yy, SSasympOff(xx, Asym = 5, lrc = log(0.4), c0 = 3/4)) ) require(graphics) op <- par(mar = c(0, 0, 4.0, 0)) plot(xx, yy, type = "l", axes = FALSE, ylim = c(-.5,6), xlim = c(-1, 8), xlab = "", ylab = "", lwd = 2, main = "Parameters in the SSasympOff model") mtext(quote(list(phi[1] == "Asym", phi[2] == "lrc", phi[3] == "c0"))) usr <- par("usr") arrows(usr[1], 0, usr[2], 0, length = 0.1, angle = 25) arrows(0, usr[3], 0, usr[4], length = 0.1, angle = 25) text(usr[2] - 0.2, 0.1, "x", adj = c(1, 0)) text( -0.1, usr[4], "y", adj = c(1, 1)) abline(h = 5, lty = 3) arrows(-0.8, c(2.1, 2.9), -0.8, c(0 , 5 ), length = 0.1, angle = 25) text (-0.8, 2.5, quote(phi[1])) segments(3/4, -.2, 3/4, 1.6, lty = 2) text (3/4, c(-.3, 1.7), quote(phi[3])) arrows(c(1.1, 1.4), -.15, c(3/4, 7/4), -.15, length = 0.07, angle = 25) text (3/4 + 1/2, -.15, quote(1)) segments(c(3/4, 7/4, 7/4), c(0, 0, 2), # 5 * exp(log(0.4)) = 2 c(7/4, 7/4, 3/4), c(0, 2, 0), lty = 2, lwd = 2) text( 7/4 +.1, 2./2, quote(phi[1]*e^phi[2]), adj = c(0, .5)) par(op) </pre> <hr /><div style="text-align: center;">[Package <em>stats</em> version 3.6.0 <a href="00Index.html">Index</a>]</div> </body></html>