docs: public static Vector toVector(INDArray arr) {
          if (!arr.isVector()) {
              throw new IllegalArgumentException("passed in array must be a vector");
          }
          // FIXME: int cast
          double[] ret = new double[(int) arr.length()];
          for (int i = 0; i < arr.length(); i++) {
              ret[i] = arr.getDouble(i);
          }
  
          return Vectors.dense(ret);
      }