Unable to plot. Problem with this error "Conversion to double from function_handle is not possible."

Question

jayash 2015-2-16

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https://ww2.mathworks.cn/matlabcentral/answers/178683-unable-to-plot-problem-with-this-error-conversion-to-double-from-function_handle-is-not-possible

回答： Adam 2015-2-16

 function f=snm(~)
 eq11= @(q1)(2*(1 - cos(2*pi*q1))); 
 hq1= @(q1,U,n0)((eq11)^2 + 2*U*n0*(eq11))^(1/2); 
 ha1= @(q1,U,n0)(((eq11) + (U*n0))/hq1) - 1; 
 f= @(U,n0)(n0 + 5/10*integral(@(q1)ha1,-0.5, 0.5));
 a=@(U)fsolve(f-0.5,0.1);
 plot(a,0,20);

I want to plot between "a" and "U", but unable to plot due to this error "Conversion to double from function_handle is not possible." . Could anyone help me out with this problem?

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Answer 1

Adam 2015-2-16

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You are attempting to plot a function handle.

The plot function expects data, not a function to evaluate.

Your definition of 'a' takes 'U' as a parameter but then ignores it. Also the syntax of

fsolve(f-0.5,0.1);

does not look correct. I don't have access to the fsolve function, but I assume it should be more like:

fsolve( f, -0.5, 0.1 )

if you are using -0.5 to 1 as your limits. Or rather, I assume you want U to be involved in there somewhere otherwise why pass it as an argument to your 'a' function?