public INDArray sub(INDArray x, INDArray y) {
    NDValidation.validateNumerical("sub", "x", x);
    NDValidation.validateNumerical("sub", "y", y);
    return Nd4j.exec(new org.nd4j.linalg.api.ops.impl.transforms.pairwise.arithmetic.SubOp(x, y))[0];
  }