National Instruments 370757C-01 用户手册

Using the system from the first example (Figure 2-3), you can compare 
the results of using the three scaling algorithms: 

MARG_PF=smargin(H,delb,{scaling="PF",!graph});

MARG_OS=smargin(H,delb,{scaling="OS",!graph});

MARG_OPT=smargin(H,delb,{scaling="OPT",!graph});

plot ([MARG_PF,MARG_OS,MARG_OPT],{xlog,

legend=["PF","OS","OPT"],xlab="Frequency, Hz.",

ylab="Stability margin, dB"})

Figure 2-8 plots the margins produced by the three scaling algorithms. 
Notice that in this problem the three scalings yield identical stability 
margins. 

Figure 2-8.  Results of Scaling Algorithm Options