I'm kinda new to Matlab

Wot i'm trying to do is draw a Bode plot without using the inbuilt 'bode' function.

i tried using logspace command for the purpose but all in vain

can anyone help???

Here is the code i had written

a=[0 0 25];

b=[1 4 25];

w=logspace(-1,2)

hold on

w1=0.1:100;

for i=1:100

x=polyval(a,j*w1(i));

y=polyval(b,j*w1(i));

z=x/y;

b=abs(z);

plot(20*log10(B),w(i),'+')

hold on

end

pls help

thx a lot