code: public static double[] plusEquals(final double[] v1, final double s1) {
      for(int i = 0; i < v1.length; i++) {
        v1[i] += s1;
      }
      return v1;
    }
docs: Computes component-wise v1 = v1 + s1,
  overwriting the vector v1.
  
  @param v1 vector to add to (overwritten)
  @param s1 constant value to add
  @return Modified vector