How to create a list of an array index

I am doing a project Euler prime number puzzle but I do not wish to use the Matlab primes function , so I'm building my own.

I am going to use the standard sieve to produce my primes but I wish to store these in a logic array. How do I get the index/cell location of all true values into an array/output as these will be my prime numbers.

Thanks

AD

Answer 1

[Image Analyst]

Can't you just use a counter that increments when you find a prime number?

if itsAPrimeNumber
    numberOfPrimesFound = numberOfPrimesFound + 1;
    listOfPrimes(numberOfPrimesFound) = yourCurrentNumber;
end

[Scragmore]

If possible I would like to do it this way, learning to do bitwise calculations, bigger array/smaller memory allocation, how I want to use the function ect.

so if I have an array;

ary = [1 1 0 1 0 1 0 0 0 1 .....]

I would like to return;

return ary(true)

ans = 2 3 5 7 11 .......

[Image Analyst]

Just do this

primesList = find(ary)+1;

The find() function tells you which elements are non-zero or true.