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.TH nyquist 1 "April 1993" "Scilab Group" "Scilab Function"
.so ../sci.an
.SH NAME
nyquist - nyquist plot
.SH CALLING SEQUENCE
.nf
nyquist( sl,[fmin,fmax] [,step] [,comments] )
nyquist( sl, frq [,comments] )
nyquist(frq,db,phi [,comments])
nyquist(frq, repf [,comments])
.fi
.SH PARAMETERS
.TP 10
sl
: \fVsyslin\fR list (SIMO linear system in continuous or discrete time )
.TP
fmin,fmax
: real scalars (frequency bounds (in Hz))
.TP
step
: real (logarithmic discretization step)
.TP
comments
: string vector (captions).
.TP
frq
: vector or matrix of frequencies (in Hz) (one row for
each output of \fVsl\fR).
.TP
db,phi
: real matrices of modulus (in Db) and phases (in degree) (one row for each output of \fVsl\fR).
.TP
repf
: matrix of complex numbers. Frequency response (one row
for aech output of \fVsl\fR)
.SH DESCRIPTION
Nyquist plot i.e Imaginary part versus Real part of the frequency
response of \fVsl\fR.
.LP
For continous time systems \fVsl(2*%i*%pi*w)\fR is plotted.
For discrete time system or discretized systems \fVsl(exp(2*%i*%pi*w*fd)\fR
is used ( \fVfd=1\fR for discrete time systems and \fVfd=sl('dt')\fR for discretized systems )
\fVsl\fR can be a continuous-time or discrete-time SIMO system (see \fVsyslin\fR).
In case of multi-output the outputs are plotted with different
symbols.
.LP
The frequencies are given by the bounds \fVfmin,fmax\fR (in Hz) or by a row-vector
(or a matrix for multi-output) \fVfrq\fR.
.LP
\fVstep\fR is the ( logarithmic ) discretization step. (see \fVcalfrq\fR for the
choice of default value).
.LP
\fVcomments\fR is a vector of character strings (captions).
.LP
\fVdb,phi\fR are the matrices of modulus (in Db) and phases (in degrees).
(One row for each response).
.LP
\fVrepf\fR is a matrix of complex numbers. One row for each response.
.LP
Default values for \fVfmin\fR and \fVfmax\fR are
\fV1.d-3\fR, \fV1.d+3\fR if \fVsl\fR is continuous-time
or \fV1.d-3\fR, \fV0.5\fR if \fVsl\fR is discrete-time.
.LP
Automatic discretization of frequencies is made by \fVcalfrq\fR.
.SH EXAMPLE
.nf
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])
.fi
.SH SEE ALSO
bode, black, calfrq, freq, repfreq, phasemag
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