how to choose K in top-K retrievement when using PRF(pseudo-relevance feedback)?

[Executedone]

Thank you for your code! I found an enhanced approach called PRF in your new paper "Context-Aware Document Term Weighting for Ad-Hoc Search", it seemed to search top-k documents for a given query and then construct relavence of one document and queries. So how to choose the number K (K=10? K=30?) , how important it is for our ground truth term weight? Thanks!

[Daniil200707]

K=10