How can I avoid using for loop in this functions
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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!
4 个评论
Rik
2023-3-26
Have you tried logical indexing?
Dyuman Joshi
2023-3-26
编辑：Dyuman Joshi
2023-3-26
Loops are quite efficient if used properly and the usage above looks good. Although you can club the 1st two conditions together -
if i~=0
k=abs(i);
y(i)=sign(i).^(k)./gamma(k+1).*(z/2).^k;
else
y(i)=-z.^2/4+1;
end
If you are dealing with floating point numbers, I would suggest you to use a tolerance to compare rather than equality.
As Rik mentions, logical indexing is another good option. If you can attach your data, we can run and test the code.
祥宇 崔
2023-3-26
祥宇 崔
2023-3-26
采纳的回答
KSSV
2023-3-26
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));
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