sigmoid_() {
        const this_data = this.data;
        for (let i = 0; i < this_data.length; ++i) {
            this_data[i] = 1 / (1 + Math.exp(-this_data[i]));
        }
        return this;
    }
Applies the sigmoid function to the tensor in place.
@returns {Tensor} Returns `this`.