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Paul Rubin's interface to R.

Works now. However, it needs additional Perl libraries, which are currently
commented out. Also, an R-package needs to be installed.

<problem>
<script type="loncapa/perl">
$seed=&random(1,500,1);
$n=&random(15,25,1);
$offset=&random(2,5,0.1);
$slope=&random(0.6,2.5,0.1);
# construct a data set using R
# dump is for debugging, print to screen to see data structure
($data,$dump)=&cas_hashref('R',"set.seed($seed);x<-1:$n;w<-1+sqrt(x)/2;data.frame(x=x,y=$offset+$slope*x+rnorm(x)*w);");
@x=&cas_hashref_array($data,'x');
@y=&cas_hashref_array($data,'y');
$datax=join(',',@x);
$datay=join(',',@y);
# calculate the right answer using R
($answerdata,$dump)=&cas_hashref('R',"x<-c($datax);y<-c($datay);dataset<-data.frame(x=x,y=y);fm<-lm(y~x,data=dataset);");
$answer=&cas_hashref_entry($answerdata,'coefficients','x').'*x+'.&cas_hashref_entry($answerdata,'coefficients','(Intercept)');
</script>

<startouttext />
Consider the plotted data set.<br />
<endouttext />
<gnuplot width="400" solid="0" plotcolor="monochrome" gridlayer="off" bmargin="default" font="9" alttag="dynamically generated plot" bgcolor="xffffff" texfont="22" transparent="off" plottype="Cartesian" rmargin="default" gridtype="Cartesian" minor_ticscale="0.5" fontface="sans-serif" grid="on" align="left" texwidth="93" height="300" border="on" samples="100" fgcolor="x000000" major_ticscale="1" tmargin="default" lmargin="default" fillstyle="empty">
    <curve linestyle="points" linetype="solid" color="x000000" pointtype="3" limit="closed" pointsize="2" linewidth="1">
        <data>@x</data>
        <data>@y</data>
    </curve>
    
</gnuplot>

<startouttext />
<br />
Give a linear function approximating the data.<br />
<tt>y(x)=</tt>
<endouttext />
<formularesponse id="11" answer="$answer" samples="x@1:$n#20">
    <responseparam name="tol" default="2%" description="Numerical Tolerance" type="tolerance" />
    <textline size="25" readonly="no" />
    
</formularesponse>
</problem>