Attempting to Plot atand function and nothing appears in plot, any suggestions?

w0 = 1;
w = [0:1:50];
q0 = 1;
y = 20*log10(sqrt((1-(w/w0).^2).^2+(w/(w0*q0)).^2));
x = atand(((w/(w0*q0)))/(1-(w/w0).^2));
plot(w,y)
grid on;
figure()
plot(w,x)

I am trying to plot second order frequency response for a particular form. I've tried using the bode and plot function to plot the phase and magnitude of a specific function for varying values of Q.

Nothing appears for the plot(w,x) I am expecting a 0 - 180 degree phase shift once w reaches 100.

Where am I going wrong? The first plot(w,y) functions as expected.

Answer 1

[dpb]

>> whos w
Name      Size            Bytes  Class     Attributes
w         1x51              408  double              
>> whos x
Name      Size            Bytes  Class     Attributes
x         1x1                 8  double              
>>

OK, why dat???

x = atand(((w/(w0*q0)))/(1-(w/w0).^2));

Aha! "/" is matrix divide or mrdivide internally.

>> help mrdivide
/   Slash or right matrix divide.
  A/B is the matrix division of B into A, which is roughly the
  same as A*INV(B) , except it is computed in a different way.
 ...

What you're looking for here is element-wise division; these are the "dot" operators in Matlab--

Use

>> x = atand(((w/(w0*q0)))./(1-(w/w0).^2));  % instead, note the "./"
>> whos x
Name      Size            Bytes  Class     Attributes

x         1x51              408  double              
>>

Now you'll see what you're expecting...

BTW, everybody has got to learn this sooner of later... :)

[Grant Griffin]

Thank you.. haha