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The question of Taylor expansion of loss function in XGBoost [duplicate]

I am learning XGBoost from documentation, but there are a few questions in the derivation of it. In the part of ...
1
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1answer
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xgboost tayler expansion detail [duplicate]

This is the objective function for Xgboost. I have no idea where $g_{i}$ and $h_{i}$ came from is some one explain how this two terms came form? or direct me to the related tutorial page then I ...
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Taylor expansion in xgboost [duplicate]

I'm reading through the math of xgboost: https://xgboost.readthedocs.io/en/latest/model.html Under the ADDITIVE TRAINING section of the objective function, I saw that in the derivation of the ...
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XGBoost Loss function Approximation With Taylor Expansion

As an example, take the objective function of the XGBoost model on the $t$'th iteration: $$\mathcal{L}^{(t)}=\sum_{i=1}^n\ell(y_i,\hat{y}_i^{(t-1)}+f_t(\mathbf{x}_i))+\Omega(f_t)$$ where $\ell$ is ...