code: private static void convolve(double[] x, double[] y, double[] out) {
  //        if (x.length != y.length || x.length != out.length)
  //                throw new IllegalArgumentException("Mismatched lengths");
          int n = x.length;
          convolve(x, new double[n], y, new double[n], out, new double[n]);
      }
docs: /*
  Computes the circular convolution of the given real vectors. Each vector's length must be the same.