Method autocorr

Compute the autocorrelation ,--, ac(i) = > x(n) x(n-i) for all n `--' for lags between 0 and lag-1, and x == 0 outside 0...n-1 @param x - in: float[0...n-1] samples x @param ac - out: float[0...lag-1] ac values @param lag @param n

(final float[] x,
                              final float[] ac,
                              int lag,
                              final int n)