I have a set of test scores with dates that I can graph. I would like to be able to include a trendline on the graph. What I wrote is not quite right  the line just follows the original  it's not straight. I would be extremely grateful for any help.
I calculated the slope thus (some subs not included):
#
# FOR SLOPE
#
my $mean_score = &average(\@allscores);
$mean_score= sprintf("%.0f",$mean_score);
my $stdev_score = &stdev(\@allscores);
$stdev_score= sprintf("%.3f",$stdev_score);
my @list_of_x;
my @list_of_y;
my @list_of_z;
my $num_scores = @allscores;
# Get list of x
# since each date is just ... yeah... 1
my $dates = 1;
foreach ($i=0; $i<$num_scores; $i++){
@list_of_x[$i] = ($dates$mean_score)/$stdev_score;
@list_of_x[$i]= sprintf("%.2f",@list_of_x[$i]);
$dates++;
}
# Get list of y
foreach ($i=0; $i<$num_scores; $i++){
@list_of_y[$i] = (@allscores[$i]$mean_score)/$stdev_score;
@list_of_y[$i]= sprintf("%.2f",@list_of_y[$i]);
}
# Get the list of zscores
for($i=0; $i<$num_scores; $i++){
@list_of_z[$i]= (@list_of_x[$i] * @list_of_y[$i]);
@list_of_z[$i]= sprintf("%.2f",@list_of_z[$i]);
}
# add up the zscores
my $sigma = 0;
for($i=0; $i<$num_scores; $i++){
$sigma = ($sigma + @list_of_z[$i]);
}
# get the correlation
my $correl = $sigma/($num_scores1);
# get the slope
my $stdev_x = &stdev(\@list_of_x);
my $stdev_y = &stdev(\@list_of_y);
my $slope = $correl * ($stdev_x / $stdev_y);
$slope= sprintf("%.2f",$slope);
# add slope to each y ... y is each score
my @trendline;
for($i=0; $i<$num_scores; $i++){
@trendline[$i] = @allscores[$i]+$slope;
@trendline[$i] = sprintf("%.4f",@trendline[$i]);
}
#create the data for transfer to the graph program
$trendlineString = join(',',@trendline);
And the graphing script does this:
my @data = ([@alldates],
[@allScores],
[@trendline]
);
my $mygraph = GD::Graph::lines>new(600, 300);
$mygraph>set(
x_label => 'Assessments',
y_label => 'Score',
title => 'Progress Monitoring Report for '.$student,
y_max_value => 100,
y_min_value => 0,
show_values => 1,
# Show the grid
long_ticks => 1,
#line_types => [1, 2, 4],
line_types => [1],
# Set the thickness of line
line_width => 4,
# Set colors for datasets
#dclrs => ['blue', 'green', 'red'],
dclrs => ['blue','red'],
) or warn $mygraph>error;
$mygraph>set_legend_font(GD::gdMediumBoldFont);
my $myimage = $mygraph>plot(\@data) or die $mygraph>error;
print "Contenttype: image/png\n\n";
print $myimage>png;
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