Method onGrad

tools/train/source/grad/ZeroGrad.cpp:19–24

        mType = LINEAR;
    }
    virtual std::vector<Express::VARP> onGrad(Express::EXPRP expr,
                                              const std::vector<Express::VARP>& backwardOutput) override {
        std::vector<Express::VARP> result(1, nullptr);
        result[0] = backwardOutput[0];
        return result;
    }
};
static void _create() {
    static ZeroGrad _c;