Unable to plot after using fsolve

Ut=0;
while Ut<20
    cn = @(q1,q2,n0)((Ut.*n0)./(1-cos(2.*pi.*q1)-cos(2.*pi.*q2)));
    y =  @(q1,q2,n0)0.25.*((1+cn(q1,q2,n0)).^(-1/2)+(1+cn(q1,q2,n0)).^(1/2)-2);
    a = -0.5;
    b = 0.5;
    v = @(n0) (quad2d(@(q1,q2) y(q1,q2,n0),a,b,a,b));
    cv =@(n0) n0+(0.5*v(n0))-1;

      x0 = 0.1;
      n = fzero(cv,x0);

plot(Ut,n,'*')
xlabel('U/t')
ylabel('n0/n')
hold on 

Ut = Ut + 1;
end

The plot should be similar looking like y=1/x but I am only getting a point. Anybody please help me out.

Answer 1

[Walter Roberson]

You forgot to tell us that you also get some output, namely

   Warning: Reached the maximum number of function evaluations (2000). The result fails the global error test. 
  > In quad2d at 244
    In @(n0)(quad2d(@(q1,q2)y(q1,q2,n0),a,b,a,b))
    In @(n0)n0+(0.5*v(n0))-1
    In fzero at 286 
  Error using fzero (line 309)
  Function value at starting guess must be finite and real.

That happens when Ut = 1 (the second iteration). The integration is failing. Are you sure the integral converges?

Answer 2

[lei kai]

there is something wrong with your function cv,when Ut=1,n = fzero(cv,x0);will error