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nyquist Scilab Group Scilab Function nyquist
NAME
nyquist - nyquist plot
CALLING SEQUENCE
nyquist( sl,[fmin,fmax] [,step] [,comments] )
nyquist( sl, frq [,comments] )
nyquist(frq,db,phi [,comments])
nyquist(frq, repf [,comments])
PARAMETERS
sl : syslin list (SIMO linear system in continuous or discrete
time )
fmin,fmax : real scalars (frequency bounds (in Hz))
step : real (logarithmic discretization step)
comments : string vector (captions).
frq : vector or matrix of frequencies (in Hz) (one row for each
output of sl).
db,phi : real matrices of modulus (in Db) and phases (in degree) (one
row for each output of sl).
repf : matrix of complex numbers. Frequency response (one row for
aech output of sl)
DESCRIPTION
Nyquist plot i.e Imaginary part versus Real part of the frequency
response of sl.
For continous time systems sl(2*%i*%pi*w) is plotted. For discrete time
system or discretized systems sl(exp(2*%i*%pi*w*fd) is used ( fd=1 for
discrete time systems and fd=sl('dt') for discretized systems ) sl can
be a continuous-time or discrete-time SIMO system (see syslin). In case
of multi-output the outputs are plotted with different symbols.
The frequencies are given by the bounds fmin,fmax (in Hz) or by a
row-vector (or a matrix for multi-output) frq.
step is the ( logarithmic ) discretization step. (see calfrq for the
choice of default value).
comments is a vector of character strings (captions).
db,phi are the matrices of modulus (in Db) and phases (in degrees). (One
row for each response).
repf is a matrix of complex numbers. One row for each response.
Default values for fmin and fmax are 1.d-3, 1.d+3 if sl is
continuous-time or 1.d-3, 0.5 if sl is discrete-time.
Automatic discretization of frequencies is made by calfrq.
EXAMPLE
xbasc();
s=poly(0,'s');
h=syslin('c',(s^2+2*0.9*10*s+100)/(s^2+2*0.3*10.1*s+102.01));
comm='(s^2+2*0.9*10*s+100)/(s^2+2*0.3*10.1*s+102.01)';
nyquist(h,0.01,100,comm);
h1=h*syslin('c',(s^2+2*0.1*15.1*s+228.01)/(s^2+2*0.9*15*s+225))
xbasc();
nyquist([h1;h],0.01,100,['h1';'h'])
xbasc();nyquist([h1;h])
SEE ALSO
bode, black, calfrq, freq, repfreq, phasemag
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