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<s-function-doc>
<s-topics>
   <s-topic>rho.weight</s-topic>
</s-topics>
<s-title>
Rho (Weight) Function 
</s-title>
<s-description>
Returns the value of <s-expression>Rho</s-expression> (weight) function as in the robust literature.  
It is called by some routines in <s-expression>lmRob</s-expression>, but not supposed to be called by  
the users directly. 
</s-description>
<s-usage>
<s-old-style-usage>
rho.weight(svals, ipsi=1, xk=1.06) 
</s-old-style-usage>
</s-usage>
<s-args-required>
<s-arg name="svals">
a numeric vector. 
</s-arg>
</s-args-required>
<s-args-optional>
<s-arg name="ipsi">
an integer. If <s-expression>ipsi</s-expression> is <s-expression>1</s-expression>, the optimal loss (weight) function will be  
used; if <s-expression>ipsi</s-expression> is <s-expression>2</s-expression>, the rescaled bisquare loss (weight) function will  
be used. 
</s-arg>
<s-arg name="xk">
the tuning constant. 
</s-arg>
</s-args-optional>
<s-value>
a vector of values of <s-expression>Rho</s-expression> function. 
</s-value>
<s-section name=" REFERENCES">

Marazzi, A. (1993):   
<it>Algorithms, routines and S functions for robust statistics, </it>
Wadsworth &#38; Brooks/Cole, Pacific Grove, CA. 
</s-section>
<s-see>
<s-function name="chi.weight1.sgm">chi.weight</s-function>,
<s-function name="psi.weight1.sgm">psi.weight</s-function>,
<s-function name="psp.weight1.sgm">psp.weight</s-function>.
</s-see>
<s-keywords>
<s-keyword>robust</s-keyword>
<s-keyword>librobust</s-keyword>
</s-keywords>
<s-docclass>
function
</s-docclass>
</s-function-doc>
