When using $D_{train}$ to refine $\theta_0$, there’re several techniques can be used to improve results:

1)	Fine-Tuning Existing Parameter by Regularization

2)	Aggregating a Set of Parameters.

3)	Fine-Tuning Existing Parameter with New Parameters.


Strategy of Fine Tuning Parameters 

This strategy uses some $\theta_0$ from some pre-trained models related to the current task as a starting point and uses $D_{train}$ to find better $\theta_0$.  

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In terms of how searching strategy is affected by prior knowledge, searching algorithm motivated few-shot learning methods can be categorized as:

1)	Refining existing parameters

2)	Refining meta-learned parameters.

3)	Learning the optimizer


Types of few-shot learning by algorithms

Wang, Y., Yao, Q., Kwok, J. T., & Ni, L. M. (2020). Generalizing from a few examples: A survey on few-shot learning. ACM computing surveys (csur), 53(3), 1-34.

Generalizing from a Few Examples: A Survey on Few-Shot Learning

Modify Search Algorithm by Refining Existing Parameters

This strategy uses meta-learners learn a $\theta_0$ on similar tasks as the few-shot task, and the few-shot task will further refine $\theta_0$. For comparison, the strategy of refining existing parameters has a fixed $\theta_0$, while this strategy dynamically learn $\theta_0$ using meta learner.

Modify Search Algorithm by Refining Meta-Learned Parameters

This strategy uses meta-knowledge to learn an optimizer, which can directly output a step size and step direction.

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