Robust Control Toolbox™

Plot multiple frequency response objects and doubles on same graph

Syntax

• uplot(G1) 
  uplot(G1,G2) 
  uplot(G1,Xdata,Ydata) 
  uplot(G1,Xdata,Ydata,...) 
  uplot(G1,linetype) 
  uplot(G1,linetype,G2,...) 
  uplot(G1,linetype,Xdata,Ydata,linetype) 
  uplot(type,G1,linetype,Xdata,Ydata,linetype) 
  H = uplot(G1) 
  H = uplot(G1,G2) 
  H = uplot(G1,Xdata,Ydata) 
  H = uplot(G1,Xdata,Ydata,...) 
  H = uplot(G1,linetype) 
  H = uplot(G1,linetype,G2,...) 
  H = uplot(G1,linetype,Xdata,Ydata,linetype) 
  

Description

uplot plots double and frd objects. The syntax is the same as the MATLAB^® plot command except that all data is contained in frd objects, and the axes are specified by type.

The (optional) type argument must be one of

Type	Description
'iv,d'	Data versus independent variable (default)
'iv,m'	Magnitude versus independent variable
'iv,lm'	log(magnitude) versus independent variable
'iv,p'	Phase versus independent variable
'liv,m'	Magnitude versus log(independent variable)
'liv,d'	Data versus log(independent variable)
'liv,m'	Magnitude versus log(independent variable)
'liv,lm'	log(magnitude) versus log(independent variable)
'liv,p'	Phase versus log(independent variable)
'r,i'	Real versus imaginary (parametrize by independent variable)
'nyq'	Real versus imaginary (parametrize by independent variable)
'nic'	Nicholas plot
'bode'	Bode magnitude and phase plot

The remaining arguments of uplot take the same form as the MATLAB^® plot command. Line types (for example,'+', 'g-.', or '*r') can be optionally specified after any frequency response argument.

There is a subtle distinction between constants and frd objects with only one independent variable. A constant is treated as such across all frequencies, and consequently shows up as a line on any graph with the independent variable as an axis. A frd object with only one frequency point always shows up as a point. You might need to specify one of the more obvious point types in order to see it (e.g., '+', 'x', etc.).

Examples

Two SISO second-order systems are created, and their frequency responses are calculated over different frequency ranges.

• a1 = [-1,1;-1,-0.5];
  b1 = [0;2]; c1 = [1,0]; d1 = 0; 
  sys1 = ss(a1,b1,c1,d1); 
  a2 = [-.1,1;-1,-0.05]; 
  b2 = [1;1]; c2 = [-0.5,0]; d2 = 0.1; 
  sys2 = ss(a2,b2,c2,d2); 
  omega = logspace(-2,2,100); 
  sys1g = frd(sys1,omega); 
  omega2 = [ [0.05:0.1:1.5] [1.6:.5:20] [0.9:0.01:1.1] ]; 
  omega2 = sort(omega2); 
  sys2g = frd(sys2,omega2);
  

An frd object with a single frequency is also created. Note the distinction between the frd object and the constant matrix in the subsequent plots.

• sys3 = rss(1,1,1);
  rspot = frd(sys3,2); 
  

The following plot uses the 'liv,lm' plot_type specification.

• uplot('liv,lm',sys1g,'b-.',rspot,'r*',sys2g);
  xlabel('log independent variable') 
  ylabel('log magnitude') 
  title('axis specification: liv,lm')
  
  
  
  
  

See Also
bode        Plots Bode frequency response

plot        Plots on linear axis

nichols     Plots Nichols frequency response

nyquist     Plots Nyquist frequency response

semilogx    Plots semi-log scale plot

semilogy    Plots semi-log scale plot

sigma       Plots singular values of a LTI system

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