The document discusses two latent dirichlet allocation (LDA) models, FB-LDA and RCB-LDA, designed to analyze public sentiment variations on Twitter and identify the reasons behind them. The FB-LDA model filters out background topics to extract foreground topics representing genuine sentiments, while the RCB-LDA ranks these topics based on their relevance and popularity. Experimental results demonstrate the effectiveness of these models in interpreting sentiment variations and suggest their potential application in other document analysis tasks.