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solve Bassel function matlab

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Carlos_conde
Carlos_conde 2017-5-17
回答： Star Strider 2017-5-17
I am trying to solve a Bessel function depending of a variable "x", for that reason I am using the fsolve command:
%%myfun
function F = myfun(x)
F = [1.5*(1-x)*besselj(0,x)-x*bessely(0,x)*(x.^2-1)];
%%main file
x0 = [0; 0];
[x,fval] = fsolve(@myfun,x0)
I do not understand what I am doing wrong.
Regards

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回答（2 个）

John D'Errico
John D'Errico 2017-5-17
myfun is a function of ONE variable, x. There is only ONE unknown, so x should be a scalar.
But if that is true, then why have you provided a VECTOR starting value in x0?
Star Strider
Star Strider 2017-5-17
You need to (1.) vectorize every multiplication and division in your function, as well as the exponentiation, and (2.) start a a point close to (not at) 0 in order to avoid fsolve throwing a ‘Objective function is returning undefined values at initial point. FSOLVE cannot continue.’ error.
This works:
myfun = @(x) 1.5*(1-x).*besselj(0,x)-x.*bessely(0,x).*(x.^2-1);
x0 = [1; 1]*eps;
[x,fval] = fsolve(myfun,x0);

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