# Help vectorising for loop for kernel density

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DoVile Last Name: 2012년 11월 24일
I am having a devil of a time figuring out how to vectorise the following for loopp
dens = NaN(length(y),1);
for i=1:length(y)
dens(i) = (1/(n*h))*sum(kernel((Y-y(i))/h));
end
Where Y has 1000 points and y has 50 points, i think perhaps it could be done by subtracting each element in y from Y such that i get a 1000 by 50 matrix. And then i can sum across columns to get the result perhaps ? but that would requre some fairly large matrices for changed dimensions and i also dont know how to do it
any help will be greatly appreciated
##### 댓글 수: 2표시숨기기 이전 댓글 수: 1
DoVile Last Name: 2012년 11월 24일
n = 1000 (number of simulated variables = length(Y), h is the bandwidth = 0.15 and the kernel function i have declared already so when the loop calls kernel(x) it should call that function, the function it self is:
K_Gauss =@(z) exp((-z.^2)./2)./sqrt(2*pi);

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### 채택된 답변

Matt Fig 2012년 11월 24일
편집: Matt Fig 2012년 11월 24일
With these values for Y and y:
Y = rand(10,1)*10;
y = rand(5,1)*10;
This gives the same result as your FOR loop:
D = (1/(n*h))*sum(kernel(bsxfun(@minus,Y.',y)/h),2);
Here is the code I used to check the equality of the two approaches, in case it helps you:
Y = rand(1000,1)*10;
y = rand(50,1)*10;
dens = NaN(length(y),1);
n = length(Y);
h = .15;
kernel = @(z) exp((-z.^2)./2)./sqrt(2*pi);
for i=1:length(y)
dens(i) = (1/(n*h))*sum(kernel((Y-y(i))/h));
end
D = (1/(n*h))*sum(kernel(bsxfun(@minus,Y.',y)/h),2);
isequal(dens,D) % Check for equality.
##### 댓글 수: 5표시숨기기 이전 댓글 수: 4
DoVile Last Name: 2012년 11월 25일
It unfortunately is not working, i accepted the answer by mistake :)
I tested the example code you posted and it works fine, however my main code still does not. I have zipped to a rar file here http://www.mediafire.com/?9o846f8f481q7sr.
Thanks alot for your help btw Matt, i am trying to get into the habbit of vectorizing my code.

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