Slider UI Control and Callback Function

Hi,

I'm having a few issues with the Slider UIControl on an existing plot. I have managed to show the following:

I don't know how to adapt the Callback function that is provided in the documentation, for my example:

b.Callback = @(es,ed) updateSystem(h,tf(wn^2,[1,2*(es.Value)*wn,wn^2]));

I would like to vary the value of FL along the Slider to automatically update the graph (the lines must stay at the exact same points), and I am expecting the higher the value of FL, the more blue points are generated as described by the criteria labelled in the following code in the comments of this question.

[johnsmithofmatlab]

    WD = 0.4;
    FL = 20;
    f=figure;
    for FK = [1.25, 1.5, 1.75, 2, 2.5, 3.5, 4, 5, 6];
    if FK == 1.25;
    y = [2 3 4 5 6 7 8 9 10 20 30 38];
    x0 = log10(40);
    x1 = log10(10000);
    y0 = log10(2); 
    y1 = log10(38);
    elseif FK == 1.5;
    y = [2 3 4 5 6 7 8 9 10 20 30 40 50 60];
    x0 = log10(12);
    x1 = log10(10000);
    y0 = log10(2); 
    y1 = log10(50);
    elseif FK == 1.75;
    y = [2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 90];
    x0 = log10(5);
    x1 = log10(10000);
    y0 = log10(2); 
    y1 = log10(90);
    elseif FK == 2;
    y = [2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 90 100];
    x0 = log10(3.5);
    x1 = log10(8000);
    y0 = log10(2); 
    y1 = log10(100);
    elseif FK == 2.5;
    y = [2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 90 100];
    x0 = log10(2.5);
    x1 = log10(5500);
    y0 = log10(2); 
    y1 = log10(100);
    elseif FK == 3.5;
    y = [2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 90 100];
    x0 = log10(1.9);
    x1 = log10(4200);
    y0 = log10(2); 
    y1 = log10(100);
    elseif FK == 4;
    y = [2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 90 100];
    x0 = log10(1.7);
    x1 = log10(3800);
    y0 = log10(2); 
    y1 = log10(100);
    elseif FK == 5;
    y = [2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 90 100];
    x0 = log10(1.5);
    x1 = log10(2800);
    y0 = log10(2); 
    y1 = log10(100);
    elseif FK == 6;
    y = [2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 90 100];
    x0 = log10(1.2);
    x1 = log10(2300);
    y0 = log10(2); 
    y1 = log10(100);
    end

    x = zeros(1,length(y));

    for i = [2:1:max(y)];
    y(i) = log10(i); 
    x(i) = x0 + (((y(i) - y0)/(y1 - y0))*(x1 - x0)); % Linear Interpolation
    x(i) = 10^(x(i));
    if x(i)*(WD) < FL; % Criteria 
       loglog(x(i),i,'c.');
          elseif x(i)*(WD) > FL;
       hold on
       loglog(x(i),i,'r.');
       xlim([1 10000]);
       ylim([1 100]);
    end
    end
    end
    grid;
    hold on
    b = uicontrol('Parent',f,'Style','slider','Position',[81,54,419,23],...
                  'value',FL, 'min',1, 'max',50);
    bgcolor = f.Color;
    bl1 = uicontrol('Parent',f,'Style','text','Position',[50,54,23,23],...
                    'String','1','BackgroundColor',bgcolor);
    bl2 = uicontrol('Parent',f,'Style','text','Position',[500,54,23,23],...
                    'String','50','BackgroundColor',bgcolor);
    bl3 = uicontrol('Parent',f,'Style','text','Position',[240,25,100,23],...
                    'String','FL','BackgroundColor',bgcolor);