My graph is empty

why my graph is empty?

if x<0
    x=[0:0.01:-x];
    xticks(0:0.01:-x) 
    a=200.*exp(-0.05.*x).*sin(x);
    b=0.8.*exp(-0.5.*x).*sin(x.*10);
    figure(1);
    plot(x,a)
    xticks(0:2:-x)
    xlabel('Zaman')
    ylabel('Frekans')
    title('Düşük Frekans')
    figure(2);
    plot(x,b)
    xlabel('Zaman')
    ylabel('Frekans')
    title('Yüksek Frekans')
    figure(3);
    yyaxis left
    plot(x,a,"b")
    ylabel('Düşük Frekans')
    yyaxis right
    plot(x,b,"r")
    title('Frekans Tepkisi')
    xlabel('Zaman')
    ylabel('Yüksek Frekans')

[Jan]

@ukulele: Please stop deleting the text of your questions after answers have been given.

Answer 1

[Walter Roberson]

if x<0
    x=[0:0.01:-x];

After the first time this code ran, negative scalar x would be replaced with a vector x that starts at 0 and increases. But then the second time you ran the code, unless you initialize x to something in previous code, then there would be no negative values in x, so the second time through the code would not pass the "if x<0" test.

[ukulele]

i solved it before i saw this comment but thanks