backwardWithGradient(grad) {
		if (Array.isArray(grad))
			this.out.dw.set(grad)
		else if (this.out.dw.length === 1)
			this.out.dw[0] = grad
		else
			throw 'error grad not propagatable';

		this.propagate()
	}
Instead of regressing the network to have minimal error, you can provide your own gradient.
@param  {Float64Array} grad