Simulated PCs from the variations of different parameters in the warm corona model. We first let the parameter Nor_nth vary randomly and there appears a principle component above the zero-line (panel A). When we further vary the parameter, Nor_comptt, the second component appears (panel B). Next, we set all the free parameters in the continuum NTHCOMP and COMPTT free to change (panel C). Finally, we vary the free parameters in the absorption model ZXIPCF and ZEDGE to see the possible influence of the absorption effect (panel D). In the figure, we also plotted the first and the second PC from real data (cyan curves) for the purpose of comparison.