sqrt(y.*conj(y))/N;

This expression calculates the magnitude of the complex vector y, normalized by the number of elements in the vector (N).

Explanation:

- `y.*conj(y)` computes the element-wise product of y with its complex conjugate, resulting in a vector of real numbers. This is equivalent to `abs(y).^2`, where `abs(y)` calculates the magnitude of y.
- `sqrt()` takes the square root of each element in the vector, resulting in a vector of positive real numbers.
- Dividing the result by N normalizes the vector by the number of elements. This is useful, for example, when calculating the average power of a signal represented by the vector y.