/* corr.c - sample cross correlation of two length-N signals */void corr(N, x, y, M, R)                  /* computes \(R[k]\), \(k = 0, 1,\dotsc, M\) */double *x, *y, *R;                        /* \(x,y\) are \(N\)-dimensional */int N, M;                                 /* \(R\) is \((M+1)\)-dimensional */{       int k, n;       for (k=0; k<=M; k++)              for (R[k]=0, n=0; n<N-k; n++)                     R[k] += x[n+k] * y[n] / N;}