can anyone help me ? i keep getting this error

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Mohamed
Mohamed 2022-9-25
评论： Torsten 2022-9-26
Here is the code:
num_roots=5; num_functions=6;
%initial guess for roots (from Wolfram MathWorld)
zeros_guess=[2.4,3.8,5.1,6,7.5,8.7;...
5.5,7,8.4,9.7,11,12;...
8.6 10,11.6,13,14,16;...
11.8,13,15,16,18,19;...
15,16.4,18,19.4,21,22];
%Compute first five roots of first six Bessel functions
%Put in variable bzeros with size(bzeros) = [5, 6]
integrand = @(theta,x,n) cos(x.*sin(theta)-n*theta);
J_n = @(x) integral(@(theta)integrand(theta,x,n),0,pi);
for n=0:num_functions-1
J_n = @(x) integral(@(theta)integrand(theta,x,n),0,pi);
for k=1:num_roots
bzeros(k,n+1)=fzero(J_n,bzeros_guess(k,n+1));
end
end
%print table
fprintf('k J0(x) J1(x) J2(x) J3(x) J4(x) J5(x)\n')
for k=1:num_roots
fprintf('%i',k)
for n=0:num_functions-1
fprintf('%10.4f',bzeros(k,n+1));
end
fprintf('\n');
end
this is the output that keeps popping out:
Undefined function 'bzeros_guess' for input arguments of type 'double'.
Error in solution (line 15)
bzeros(k,n+1)=fzero(J_n,bzeros_guess(k,n+1));
what does this mean and is there a way i can rewrite the white section so that it works ?

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采纳的回答

Chunru
Chunru 2022-9-26
Ran in:
num_roots=5; num_functions=6;
%initial guess for roots (from Wolfram MathWorld)
zeros_guess=[2.4,3.8,5.1,6,7.5,8.7;...
5.5,7,8.4,9.7,11,12;...
8.6 10,11.6,13,14,16;...
11.8,13,15,16,18,19;...
15,16.4,18,19.4,21,22];
%Compute first five roots of first six Bessel functions
%Put in variable bzeros with size(bzeros) = [5, 6]
integrand = @(theta,x,n) cos(x.*sin(theta)-n*theta);
J_n = @(x) integral(@(theta)integrand(theta,x,n),0,pi);
for n=0:num_functions-1
J_n = @(x) integral(@(theta)integrand(theta,x,n),0,pi);
for k=1:num_roots
%bzeros(k,n+1)=fzero(J_n,bzeros_guess(k,n+1));
bzeros(k,n+1)=fzero(J_n, zeros_guess(k,n+1)); % initial guess at the right hand side
end
end
%print table
fprintf('k J0(x) J1(x) J2(x) J3(x) J4(x) J5(x)\n')
k J0(x) J1(x) J2(x) J3(x) J4(x) J5(x)
for k=1:num_roots
fprintf('%i',k)
for n=0:num_functions-1
fprintf('%10.4f',bzeros(k,n+1));
end
fprintf('\n');
end
1
2.4048 3.8317 5.1356 6.3802 7.5883 8.7715
2
5.5201 7.0156 8.4172 9.7610 11.0647 12.3386
3
8.6537 10.1735 11.6198 13.0152 14.3725 15.7002
4
11.7915 13.3237 14.7960 16.2235 17.6160 18.9801
5
14.9309 16.4706 17.9598 19.4094 20.8269 22.2178
  2 个评论
Torsten
Torsten 2022-9-26
The Bessel functions are predefined in MATLAB. If it's not explicitly stated in your assignment, you don't need to evaluate them using the integral representation:
https://de.mathworks.com/help/matlab/ref/besselj.html

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