网上找的绘图的小软件Select data series on left panel [Points]. Select menu item . The 'Find the best line' Wizard appears. On step 1 choose X and Y ranges and weighting scheme. On step 2 select 'Find equation' item 'Y=f(X)'. On step 4 select 'All functions', and select 'Fourier' item unchecked. On step 5 click Start. Fitting process runs. New graphs appears. See how fit curves conform your data. Select the number of best fit functions '3' to plot. Select menu item .