nyquist(1)

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. 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 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