why is my plot not showing anything

close all;
clc
q=1;
beta=0.28;
teta=30*pi/180;
a=1;
mu=0.72;
k=2;
c=300;
for v0=80:0.5:180;
  u0=v0-10;
  alfa1=mu*(k-1/2)/(k-3/2);
  alfa2=mu*(k-1/2)*(k+1/2)/(2*(k-3/2)^2);
  gama1=(1+3*a*u0^2)/(2*c^2);
  eta1=1+3*a*v0^2/(2*c^2);
  x1=alfa1;
  x2=-2*alfa1*u0*cos(teta)+2*alfa1*v0*cos(teta);
  x3=-q*beta*cos(teta)^2/eta1-cos(teta)^2/gama1+alfa1*u0^2*cos(teta)^2+alfa1*v0^2*cos(teta)^2+4*alfa1*v0*u0*cos(teta)^2;
  x4=2*u0*q*beta*cos(teta)^3/eta1+2*v0*cos(teta)^3/gama1-2*alfa1*v0^2*cos(teta)^3*u0-2*alfa1*v0*u0^2*cos(teta)^3;
  x5=-q*beta*cos(teta)^4*u0^2/eta1-v0^2*cos(teta)^4/gama1+alfa1*v0^2*u0^2*cos(teta)^4;
  y=[x1,x2,x3,x4,x5];
  landa=roots(y);
  if isreal(landa(4))
      plot(v0,landa(4));
      hold on;
  end
end

Answer 1

[Azzi Abdelmalek]

landa is always a complex number.

[Mohammad Alavi]

Hi . what id do now ?I'm a little confused on this issue .

[Azzi Abdelmalek]

Do you want to plot only real roots?

[Mohammad Alavi]

Yes : i should see two figure by real number from landa.

[Azzi Abdelmalek]

Ok,landa contains only complex numbers. What do you want to do with them?

Answer 2

[Walter Roberson]

There are no real roots in the range v0 = 80 to 180. The two real roots are

v0 = -2.9519709800851799940292844879542507513708021691910
v0 = 22.904282241682175870334381209712496165896259534707

The equation is a quartic in which only two of the roots are real. By the range v0 80 to 180, the imaginary components are unquestionably non-zero .