static double[] secti( double[] v1, double[] v2 ) {
     int n = v1.length > v2.length ? v1.length : v2.length;
     double[] s = new double[n];
     for( int i = 0; i < v1.length; i++ ) {
        s[i] = v1[i];
     }
     for( int i = 0; i < v2.length; i++ ) {
        s[i] += v2[i];
     }
     return s;
  }