I to create a function using besselj function and solve it using fzero to find eigenvalues like this...

t = 1:.01:30;
x = t;
y = besselj(1,t);

t = 1:.01:30;
b = 10;
y2 = besselj(0,t);

x0=[0 30];
fun = t.*y - b.*y2 ;
z = fzero(fun, x0)

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Whe I try to put this code at the MatLab it shows this message: Error using fzero (line 169) FUN must be a function, a valid string expression, or an inline function object.

Error in Try6 (line 9) z = fzero(fun, x0)

Answer 1

[Walter Roberson]

Symbolically you seem to be trying to solve

t * BesselJ(1,t) - 10 * BesselJ(0,t)

probably for t. If that is the case, then code

fzero(@(t) t .* besselj(1,t) - 10 * besselj(0,t), x0)

Note: there are 10 zeros between 0 and 30, and fzero does not promise to find the first. It might refuse to find any because the expression is negative at both 0 and 30 and so fzero would not know that there is a zero crossing.

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Thanks a lot for your help, but do you know how to show the ten first values using this equation?

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I mean...I am looking for the first ten values that solve this equation. Symbolically I want to find the eigenvalues....that are found using that equation...

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I discovered that this function just gets one value per interval...do you know if I can get through ten different answers?

[Walter Roberson]

There is no nice closed form for the zeros of Bessel functions.

For numeric solutions see http://www.mathworks.com/matlabcentral/answers/103169-how-do-i-find-all-the-zeros-of-a-function

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Thanks a lot!! But I also used this code: a = 0:30; for x0 = 1:length(a) t = 1:.01:10; z = x0; z = fzero(@(t) t .* besselj(1,t) - 10 * besselj(0,t), x0) end

with the above code I found all the values that I want. But some values show up more than once. Do you know how to do it to they show up only once?