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<table width="100%" summary="page for rms.curv {MASS}"><tr><td>rms.curv {MASS}</td><td align="right">R Documentation</td></tr></table>
<h2>Relative Curvature Measures for Non-Linear Regression</h2>
<h3>Description</h3>
<p>
Calculates the root mean square parameter effects and intrinsic relative
curvatures, <i>c^theta</i> and <i>c^iota</i>, for a fitted nonlinear regression, as
defined in Bates & Watts, section 7.3, p. 253 et seq.
</p>
<h3>Usage</h3>
<pre>
rms.curv(obj)
</pre>
<h3>Arguments</h3>
<table summary="R argblock">
<tr valign="top"><td><code>obj</code></td>
<td>
Fitted model object of class <code>"nls"</code>. The model must be fitted using the
default algorithm.
</td></tr>
</table>
<h3>Details</h3>
<p>
The method of section 7.3.1 of Bates & Watts is implemented. The
function <code>deriv3</code> should be used generate a model function with first
derivative (gradient) matrix and second derivative (Hessian) array
attributes. This function should then be used to fit the nonlinear
regression model.
</p>
<p>
A print method, <code>print.rms.curv</code>, prints the <code>pc</code> and
<code>ic</code> components only, suitably annotated.
</p>
<p>
If either <code>pc</code> or <code>ic</code> exceeds some threshold (0.3 has been
suggested) the curvature is unacceptably high for the planar assumption.
</p>
<h3>Value</h3>
<p>
A list of class <code>rms.curv</code> with components <code>pc</code> and <code>ic</code>
for parameter effects and intrinsic relative curvatures multiplied by
sqrt(F), <code>ct</code> and <code>ci</code> for <i>c^theta</i> and <i>c^iota</i> (unmultiplied),
and <code>C</code> the C-array as used in section 7.3.1 of Bates & Watts.</p>
<h3>References</h3>
<p>
Bates, D. M, and Watts, D. G. (1988)
<EM>Nonlinear Regression Analysis and its Applications.</EM>
Wiley, New York.
</p>
<h3>See Also</h3>
<p>
<code><a href="../../stats/html/deriv.html">deriv3</a></code>
</p>
<h3>Examples</h3>
<pre>
# The treated sample from the Puromycin data
mmcurve <- deriv3(~ Vm * conc/(K + conc), c("Vm", "K"),
function(Vm, K, conc) NULL)
Treated <- Puromycin[Puromycin$state == "treated", ]
(Purfit1 <- nls(rate ~ mmcurve(Vm, K, conc), data = Treated,
start = list(Vm=200, K=0.1)))
rms.curv(Purfit1)
##Parameter effects: c^theta x sqrt(F) = 0.2121
## Intrinsic: c^iota x sqrt(F) = 0.092
</pre>
<hr><div align="center">[Package <em>MASS</em> version 7.2-44 <a href="00Index.html">Index]</a></div>
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