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db, phaseb

Purpose

Compute the decibel magnitude.
Compute the unwrapped phase in degrees.

Syntax

m = db(xf)
p = phaseb(xf)

Description

db computes the decibel magnitude of each element of the matrix xf. An equivalent would be

 m = 20*log10(abs(xf))

phaseb is an extension to the case of multiple FRF stacked as columns of a matrix xf of the phase routine available in the System Identification Toolbox. It computes the phase in degrees with an effort to keep the phase continuous for each column.

Example

Here is an example that generates the two FRF of a SIMO system and plots their magnitude and phase.

 a=[0 1;-1 -.01];b=[0;1];c=[1 0;0 1];d=[0;0];
 w=linspace(0,2,100)'; xf=qbode(a,b,c,d,w);
figure(10); clf;
 subplot(211);plot(w,dbsdt(xf));    title('dB magnitude') 
 subplot(212);plot(w,phaseb(xf));title('Unwrapped phase in degrees')

See also

The xf format, iiplot