Task

Write a boolean function that tells whether a given integer is prime.



Remember that   1   and all non-positive numbers are not prime.

Use trial division.

Even numbers greater than   2   may be eliminated right away.

A loop from   3   to   √ n    will suffice,   but other loops are allowed.



Related tasks

   count in factors
   prime decomposition
   AKS test for primes
   factors of an integer
   Sieve of Eratosthenes
   factors of a Mersenne number
   trial factoring of a Mersenne number
   partition an integer X into N primes
   sequence of primes by Trial Division


function isPrime = primalityByTrialDivision(n)
 
    if n == 2
        isPrime = true;
        return
    elseif (mod(n,2) == 0) || (n <= 1)
        isPrime = false;
        return
    end
 
    %First n mod (3 to sqrt(n)) is taken. This will be a vector where the
    %first element is equal to n mod 3 and the last element is equal to n
    %mod sqrt(n). Then the all function is applied to that vector. If all
    %of the elements of this vector are non-zero (meaning n is prime) then
    %all() returns true. Otherwise, n is composite, so it returns false.
    %This return value is then assigned to the variable isPrime.
    isPrime = all(mod(n, (3:round(sqrt(n))) ));
 
end