Calculating Euler phi function

[paton51]

How do i comput the euler phi function of a large interger?
i know that if p is prime then phi(p)=p-1 and I've found a formula for computing non primes but i don't know how to implement in something like Matlab.
Does anyone know how?

 

[Werg22]

AFAIK, computing the Euler phi function requires you to know the prime factorization of the input. Unless you can find it, there's not much you can do.

 

[paton51]

Yes i know the factorisation problem is hard. I am workin with RSA encryption so we know two large primes, the product of which is N this is what i want to do euler phi on.
Since N is the product of two primes (p and q) is phi(N) simply (p-1)(q-1)?

 

[Office_Shredder]

That's right. In general

http://en.wikipedia.org/wiki/Euler's_totient_function#Computing_Euler.27s_function