How can I avoid using for loop in this functions

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祥宇崔 2023-3-26

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https://ww2.mathworks.cn/matlabcentral/answers/1935254-how-can-i-avoid-using-for-loop-in-this-functions

评论：祥宇崔 2023-4-11

This is the function whose speed I want to improve. I know I should use more matrix operation and use less for loop. But I have no idea how to use if-else in matrices.

function y=Besselj_approx(n,z)
y=zeros(1,length(n));
for i=n
    if i>0
        y(i)=1./gamma(i+1).*(z/2).^i;
    elseif i<0
        y(i)=(-1).^(-i)./gamma(-i+1).*(z/2).^(-i);
    else
        y(i)=-z.^2/4+1;
    end
end

Any help is appreciated!

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祥宇崔 2023-3-26

@Dyuman Joshi Thanks! Guess the for loop is alright.

祥宇崔 2023-3-26

@Rik Thanks! I will give it a try.

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采纳的回答

KSSV 2023-3-26

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1935254-how-can-i-avoid-using-for-loop-in-this-functions#answer_1201114

在 MATLAB Online 中打开

function y=Besselj_approx(n,z)
i = n ;
y=zeros(1,length(n));
y(1:end)=-z.^2/4+1;
y(i>0) = 1./gamma(i(i>0)+1).*(z/2).^i(i>0);
y(i<0)=(-1).^(-i(i<0))./gamma(-i(i<0)+1).*(z/2).^(-i(i<0));