Matlab does not plot the function

I'm trying to plot this function. There is no syntaxis mistakes, but the graphic appears empty. (It is a bode diagram).

GH_num= [1 2 3];
GH_den=  [4 5 6 7 8];
GH_w=[];

for w=2*pi*logspace(-1,3,1000)
        GH_num_w=polyval(GH_num,w*j);
        GH_den_w=polyval(GH_den,w*j);
        GH_w=[GH_w,GH_num_w/GH_den_w];
end

mag = 20*log10(abs(GH_w));
phase=rad2deg(angle(GH_w));

fGH=figure;
aGH=subplot(2,1,1,'Parent'fGH);
bGH=subplot(2,1,2,'Parent'fGH);
semilogx=(aGH,w/2/pi,mag)
semilogx=(bGH,w/2/pi,phase)

Answer 1

[Walter Roberson]

GH_num= [1 2 3];
GH_den=  [4 5 6 7 8];
GH_w=[];

wvals = 2*pi*logspace(-1,3,1000);      %NEW
for w = wvals                          %CHANGED
        GH_num_w=polyval(GH_num,w*j);
        GH_den_w=polyval(GH_den,w*j);
        GH_w=[GH_w,GH_num_w/GH_den_w];
end

mag = 20*log10(abs(GH_w));
phase=rad2deg(angle(GH_w));

fGH=figure;
aGH=subplot(2,1,1,'Parent',fGH);   %FIXED
bGH=subplot(2,1,2,'Parent',fGH);   %FIXED
semilogx(aGH,wvals/2/pi,mag)       %FIXED
semilogx(bGH,wvals/2/pi,phase)     %FIXED

[Inés Bodoque]

Thank you so much!