Select Code to Download

use strict;
use warnings;
...
    my ($x, $L, $x0) = @_;
    reduce{ $a+$b }map{ $L->[$_] * xdi($x,$x0,$_) }keys @$x
}

use Chart::Gnuplot;
use List::Util q(reduce);
...
my $pts = Chart::Gnuplot::DataSet->new(xdata => $xx, ydata => $ff, sty
+le => "lines");

Chart::Gnuplot->new(title => "f(x)", output => "plot.ps")->plot2d($pts
+0, $pts);