National Instruments 370757C-01 用户手册

You can compare this margin to that of the example in the 

 section; the following inputs produce Figure 2-7.

plot ([marg,margSVD],{xlog}

legend=["PF_SCALE","SVD"], 

ylab="Stability Margin,dB", 

xlab="Frequency, Hz."})

Figure 2-7.  pfscale( ) versus svd Stability Margins

The singular value approach gives results that are too conservative, suggesting that 

the uncertainties can destabilize the system. Conversely, you know from the scaled singular 
value calculations that the system is robustly stable.

In [Saf82] and [Doy82], the inequality

(2-5)

is noted. This optimization problem can be shown to be 
unimodal—for D > 0, an assumption that can be made without loss 

σ

1

–

(

) μ M

( )

≥