simple function plot in MATLAB

Hi,

I want to plot two function

1. θ=tan^(-1)〖(ω*Q_P)/ω_P 〗-tan^(-1)〖(ω/(ω_p*Q_P ))/(1-〖(ω/ω_P )〗^2 )〗

Want to plot θ w.r.t ω/ω_p. I wrote the code

 for Qp=1:1:5;
     x= 0:0.4:2;
     c=atand(x*Qp);
     f=x*power(Qp,-1);
     h=1-power(x,2);
     j=f/h;
     d=atand(j);
     o=c-d;
     plot(x,o),
     grid on,
     hold on,
 end

So ω/ω_p=x will vary from 0 to 2 and θ=o. Will get 5 graph from different value of Qp (1 to 5) The line "o=c-d" is not working. getting wrong plot. Is there anything wrong with the array? or what?

2. V_o/V_i =1/√(〖(1-(ω/ω_p )^2)〗^2+(〖ω/(ω_P*Q_P ))〗^2 )

Want to plot V_o/V_i w.r.t ω/ω_p. I wrote the code

 for Qp=1:1:5;
     x=0.5:0.01:1.5;
     d=power((1-power(x,2)),2);
     p=power((x*power(Qp,-1)),2);
     y=1\sqrt(d+p);
     % z=power(y,-1);
     plot(x,z),
     grid on,
     hold on,
  end

ω/ω_p=x will vary from 0.5 to 1.5. Will get 5 graph from different value of Qp (1 to 5)

V_o/V_i should be Y. But then the graph is not the proper one. If I inverse the graph Y ie Z then I am getting the proper graph.

** can anyone help me in this regard? Thanks San

[Geoff Hayes]

Sanjida - for the first example, you state that the line "o=c-d" is not working. getting wrong plot. What is wrong with this plot? What should the correct one be? You are using atand which expects degree inputs. Is your code providing the inputs in the correct units of degrees?

Answer 1

[VBBV]

Hi  @Sanjida

Use element wise division for evaluatiing the vector Y, It seems you have used incorrect operator ' \ ' this is meant for taking inverse of matrix, which in your case is just scalar 1 , so effectively its not doing any inverse at all. Also, for the first graph , you need to plot the phase angle, using a marker since you were to plot scalars through plot function inside a loop.

figure(1)
for Qp=1:1:5;
     x=0.5:0.01:1.5;
     d=power((1-power(x,2)),2);
     p=power((x*power(Qp,-1)),2);
     y=1./sqrt(d+p);    % use a element wise division operator for evaluating y 
     plot(x,y);
     grid on,
     hold on,     
 end
 legend({'Q = 1','Q = 2','Q = 3','Q = 4','Q = 5'})
 hold off

 % try with finer frequency ratios, 
 figure(2)
  for Qp=1:1:5;
     x= 0:0.01:2;
     c=atand(x*Qp);
     f=x*power(Qp,-1);
     h=1-power(x,2);
     j=f/h;
     d=atand(j);
     o(Qp,:)=c-d;     
  end
  plot(x,o),
  legend({'Q = 1','Q = 2','Q = 3','Q = 4','Q = 5'},'location','best')
  grid on,