#!/usr/bin/perl
$_=<>;
chomp;
@fields=split;
die "a minimum of 3 column expected.\n" if (@fields<3);
$xin=1;
$xin=@fields-3 if @fields < 5;
$xin=4 if @fields > 6;

$yin=$xin+1; $zin=$xin+2;

$sfx=$fields[$xin]; $sfy=$fields[$yin]; $sfz=$fields[$zin];
$sqfx=$fields[$xin]*$fields[$xin]; 
$sqfy=$fields[$yin]*$fields[$yin]; 
$sqfz=$fields[$zin]*$fields[$zin];
$nda=1;

print "force values for the first record: $sfx, $sfy, $sfz\n";

while(<>)
{
@fields=split;
$sfx+=$fields[$xin]; $sfy+=$fields[$yin]; $sfz+=$fields[$zin];
$sqfx+=$fields[$xin]*$fields[$xin]; 
$sqfy+=$fields[$yin]*$fields[$yin]; 
$sqfz+=$fields[$zin]*$fields[$zin];
$nda++;
}

$avef=($sfx+$sfy+$sfz)/$nda;
$rmsf=sqrt(($sqfx+$sqfy+$sqfz)/$nda-$avef*$avef);
print "RMSF: $rmsf\n";

