how to make a function that take an integer as input and return ture if this prime otherwise false

Question

Muhammad Usman Saleem 2015-5-28

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https://ww2.mathworks.cn/matlabcentral/answers/219994-how-to-make-a-function-that-take-an-integer-as-input-and-return-ture-if-this-prime-otherwise-false

回答： charu sharma 2015-8-20

Hi everyone; I am going to attempt that question: Write a function myprime that takes n, a positive integer, as an input and returns true if n is prime or returns false otherwise. Do not use the isprime or primes or factor built-‐in functions. Hint: you can use the rem or fix functions. I am using that code

function prime=myprime(n)
a=abs(n);
i=1;
while i<a
    if rem(a,i)~=0
        prime='TURE';
    else
        prime='FALSE';
    end
    i=i+1;
end
end

and getting error

      Feedback: Your function made an error for argument(s) 2
      Your solution is _not_ correct.

Guide me where i need corrections in my code. Thanks in advance for assistance..

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Muhammad Usman Saleem 2015-5-28

yes i am bound to not use build in function @ B.k

Ryan Livingston 2015-5-28

I removed the product tag for "MATLAB Coder" below since this example is not using the product MATLAB Coder. Please only use that product tag when this product is involved. Thank you.

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Answer 1

Andrei Bobrov 2015-5-28

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在 MATLAB Online 中打开

function p = myprime(n)
p = n-nnz(rem(n,1:n)) == 2;

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Muhammad Usman Saleem 2015-5-28

@Andrei thanks for contributions... Please mark comments in 2nd line of your code so that i can understand what is actual manipulating here

Andrei Bobrov 2015-5-29

在 MATLAB Online 中打开

a = rem(n,1:n) % determining the remainder of division n on a series of numbers 1: n
b = nnz (a); % the number of divisions with remainder
out = n-2 == b;  % condition for prime number

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Answer 2

B.k Sumedha 2015-5-28

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https://ww2.mathworks.cn/matlabcentral/answers/219994-how-to-make-a-function-that-take-an-integer-as-input-and-return-ture-if-this-prime-otherwise-false#answer_180766

在 MATLAB Online 中打开

function result = isprime2(number)
number=5;
result=true;
%%check if number is a nonnegative integer
if floor(number)~=number || number<0
    result=false;
    return
end
%%check if number can be divided by another integer
for k=2:(number/2)
    if rem(number,k)==0
        result=false;
        return
    end
end

Returns 1 if the number isprime and returns 0 if the number is not prime.

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Muhammad Usman Saleem 2015-5-28

在 MATLAB Online 中打开

@B.k Sumedha thanks for contribution i am now using that code

function result = myprime(n)
n=5;
result=true;
if floor(n)~=n || n<0
    result=false;
    return
end
for k=2:(n/2)
    if rem(n,k)==0
        result=false;
        return
    end
end

but when i test this code i got an error

Feedback: Your function performed correctly for argument(s) 2
    Feedback: Your function performed correctly for argument(s) 3
    Feedback: Your function made an error for argument(s) 4
      Your solution is _not_ correct.

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Answer 3

charu sharma 2015-8-20

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https://ww2.mathworks.cn/matlabcentral/answers/219994-how-to-make-a-function-that-take-an-integer-as-input-and-return-ture-if-this-prime-otherwise-false#answer_189892

For number n being prime, if it is divisible by any of the numbers from 2 to n/2 then it is not prime so you just need to check the divisibility till n/2. MATLAB uses 0 or 1 in place of false and true. You can refer this too for less time complexity: http://farzicoders.blogspot.in/2015/08/write-function-myprime-that-takes-n.html