about prime matlab problem

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Maria 2020-6-19

0
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评论： Maria 2020-6-19

hey ! for my code below, I think I avoid "1" for prime number, but it seems like the output still show 1 as an prime number. How should I fix it? Like if you print out [1 3 4 88 5 ], it only returns 3, 5 but here it returns 1,3,5. Can someone help to fix?

function primeVec = vecOfPrimes(vec)
k = 1;
for i=1:length(vec)
n = vec(i);
flag = 1;
for j=2:sqrt(n)
if mod(n, j) == 0
flag = 0;
break
end
end
if flag == 1
primeVec(k) = n;
k = k + 1;
end
end
end

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Answer 1

the cyclist 2020-6-19

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https://ww2.mathworks.cn/matlabcentral/answers/551464-about-prime-matlab-problem#answer_454411

在 MATLAB Online 中打开

The reason is that if an element of vec is equal to 1, then

for j=2:sqrt(n)

is

for j=2:1

so that for loop is never entered, and you do not flip flag to zero.

You might need to consider 1 as a special case.

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the cyclist 2020-6-19

No offense, but it seems a little surprising to me that you know how to write the logic of the above code, but cannot then figure out this last little bit.

Is your homework to simply modify this code that was provided to you?

I'm happy to help, but if this is homework, it would be better for your learning if I give you a hint, rather than the straight-up answer.

Maria 2020-6-19