use constant eps => 0.00001;   
my $m;   

sub eigen {
	$m = shift;   # assume a Math::MatrixReal object
	return _eigen(-1e300, $m->column(1)->each(sub{1}));	  
}
sub _eigen {
	my $v = $_[1]; 
	$v = $m*$v;   
	my $eigen = $v->norm_max();   
	$v = $v*(1/$eigen);  
	abs($eigen - $_[0]) > eps ? _eigen($eigen,$v) : return($eigen,$v);
}