Table 2. The most important 20 feature lines evaluated by IW-PCA.

Feature number index	Line Wavelength (/nm)	Corresponding element	Normalized importance weight	Feature number index	Line Wavelength (/nm)	Corresponding element	Normalized importance weight
1	279.5	Ca	0.022	11	656.3	H	0.159
2	279.8	Ca	0.015	12	744.6	N	0.006
3	393.4	Ca	0.246	13	746.6	N	0.021
4	396.8	Ca	0.162	14	766.5	K	1.000
5	422.7	Ca	0.033	15	769.9	K	0.647
6	430.3	Ca	0.005	16	777.4	O	0.135
7	445.5	Ca	0.005	17	818.5	N	0.015
8	517.7	Fe	0.004	18	821.6	N	0.017
9	589.0	Na	0.945	19	844.6	O	0.006
10	589.6	Na	0.599	20	854.5	H	0.006