What is the use of base_score in xgboost multiclass working?

问题

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This bounty is for a reproducible example illustrating the application of base_score or base_margin to a multiclass XGBoost classification problem (softmax or softprob) using R.

I am trying to explore the working of Xgboost binary classification as well as for multi-class. In case of binary class, i observed that base_score is considered as starting probability and it also showed major impact while calculating Gain and Cover.

In case of multi-class, i am not able to figure out the importance of base_score parameter because it showed me the same value of Gain and Cover for different(any) values of base_score.

Also i am unable to find out why factor of 2 is there while calculating cover for multi-class i.e. 2*p*(1-p)

Can someone help me on these two parts?

来源：https://stackoverflow.com/questions/62350750/what-is-the-use-of-base-score-in-xgboost-multiclass-working