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        $enthalpy += $thermo_values{$_}{enthalpy};
        $entropy += $thermo_values{$_}{entropy};
    }
    # Account for initiation parameters
    $enthalpy += $thermo_values{substr($sequence,  0, 1)}{enthalpy};
    $entropy  += $thermo_values{substr($sequence,  0, 1)}{entropy};
    $enthalpy += $thermo_values{substr($sequence, -1, 1)}{enthalpy};
    $entropy  += $thermo_values{substr($sequence, -1, 1)}{entropy};
    # Symmetry correction
    $entropy -= 1.4;
    my $r = 1.987; # molar gas constant
    my $tm = $enthalpy * 1000 / ($entropy + ($r * log($oligo_conc))) - 273.15 + (12* (log($salt_conc)/log(10)));

    return $tm;
 }

=head2 Tm_estimate

 Title   : Tm_estimate
 Usage   : my $tm = $primer->Tm_estimate(-salt => 0.05);
 Function: Estimate the Tm (melting temperature) of the primer
 Returns : A scalar containing the Tm.
 Args    : -salt set the Na+ concentration on which to base the calculation.
 Notes   : This is only an estimate of the Tm that is kept in for comparative
           reasons. You should probably use Tm instead!

           This Tm calculations are taken from the Primer3 docs: They are
           based on Bolton and McCarthy, PNAS 84:1390 (1962) 
           as presented in Sambrook, Fritsch and Maniatis,
           Molecular Cloning, p 11.46 (1989, CSHL Press).

           Tm = 81.5 + 16.6(log10([Na+])) + .41*(%GC) - 600/length

           where [Na+] is the molar sodium concentration, %GC is the
           %G+C of the sequence, and length is the length of the sequence.

           However.... I can never get this calculation to give me the same result
           as primer3 does. Don't ask why, I never figured it out. But I did 
           want to include a Tm calculation here because I use these modules for 
           other things besides reading primer3 output.

           The primer3 calculation is saved as 'PRIMER_LEFT_TM' or 'PRIMER_RIGHT_TM'
           and this calculation is saved as $primer->Tm so you can get both and
           average them!

=cut

sub Tm_estimate {

    # This should probably be put into seqstats as it is more generic, but what the heck.

    my ($self, %args) = @_;
    my $salt = 0.2;
    if ($args{'-salt'}) {
        $salt = $args{'-salt'}
    };
    my $seqobj = $self->seq();
    my $length = $seqobj->length();
    my $seqdata = Bio::Tools::SeqStats->count_monomers($seqobj);
    my $gc=$$seqdata{'G'} + $$seqdata{'C'};
    my $percent_gc = ($gc/$length)*100;

    my $tm = 81.5+(16.6*(log($salt)/log(10)))+(0.41*$percent_gc) - (600/$length);

    return $tm; 
} 

=head2 primary_tag, source_tag, location, start, end, strand...

The documentation of L<Bio::SeqFeature::Generic> describes all the methods that
L<Bio::SeqFeature::Primer> object inherit.

=cut

1;