Unable to plot after using fsolve

Question

jayash 2015-5-7

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/215649-unable-to-plot-after-using-fsolve

回答： lei kai 2015-5-8

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.

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Answer 1

Walter Roberson 2015-5-8

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/215649-unable-to-plot-after-using-fsolve#answer_178322

在 MATLAB Online 中打开

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.