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#!/usr/bin/perl
use strict;
use warnings;
use utf8;
use Fourier;
my ($filename) = @ARGV;
defined($filename) or die "USAGE: $0 filename\n";
my $labeln = "site <gs|n|gs>";
my @n = loadVector($filename, $labeln);
my $averageN = computeAverage(\@n);
my $labelNn = "<gs|n;n|gs>";
my @Nn = Fourier::loadMatrix($filename, $labelNn);
my @nq = Fourier::fourierTransform(\@Nn);
correctNqZero(\@nq, $averageN);
Fourier::printArray(\@nq);
# Here we n_{q=0}Corrected = n_{q=0} -L*n^2,
sub correctNqZero
{
my ($nq, $average) = @_;
my $val = $nq->[0]->[0];
if (!defined($val)) {
print STDERR "$0: Could not correct nq[0], it does not exist\n";
return;
}
my $nsites = scalar(@$nq);
my $correction = $nsites*$average*$average;
$nq->[0]->[0] = $val - $correction;
}
sub loadVector
{
my ($file, $label) = @_;
open(FILE, "<", "$file") or die "$0: Cannot open $file : $!\n";
my $found = 0;
while (<FILE>) {
next if (/cmdline:/i);
if (/^\Q$label/) {
$found = 1;
last;
}
}
if (!$found) {
close(FILE);
die "$0: Cannot find $label in $file\n"
}
my @v;
while (<FILE>) {
my @temp = split;
last unless (scalar(@temp) == 3);
$v[$temp[0]] = $temp[1];
}
close(FILE);
print STDERR "$0: Read vector $label from $file with ".scalar(@v)." entries.\n";
return @v;
}
sub computeAverage
{
my ($v) = @_;
my $n = scalar(@$v);
my $sum = 0;
for (my $i = 0; $i < $n; ++$i) {
$sum += $v->[$i];
}
return $sum/$n;
}
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