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speeding up my for loop

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%My challenge is to find the number of divisors for a number without using "divisors" inbuild function
%this program will work but it's taking too much time for big numbers
%I read about vectorization to reduce the time but found stucked
%help!!!
function y=divisors1(N)
sum=0;
for i=1:floor(N/2)
if lcm(N,i)==N
sum=sum+1;
end
end
y=1+sum;

Accepted Answer

Bruno Luong
Bruno Luong on 27 Feb 2021
Edited: Bruno Luong on 27 Feb 2021
function y=divisors2(N)
f = factor(N);
[~,~,J] = unique(f);
n = accumarray(J,1);
y = prod(n+1);
end
Test
>> N=27022021
N =
27022021
>> divisors2(N)
ans =
8

More Answers (1)

Alan Stevens
Alan Stevens on 27 Feb 2021
Is this any quicker?
function y = divisors1(N)
i = 1:floor(N/2);
L = lcm(N,i);
y = sum(L==N) + 1;
end
  1 Comment
Abhishek Sharma
Abhishek Sharma on 27 Feb 2021
Thanks Alan. Since the iterations haven't changed ,it still stucks for big numbers.

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