Scilab Function

nyquist - nyquist plot

Calling Sequence

nyquist( sl,[fmin,fmax] [,step] [,comments] [,f_unit])
nyquist( sl, frq [,comments] [,f_unit])
nyquist(frq,db,phi [,comments] [,f_unit])
nyquist(frq, repf [,comments] [,f_unit])

Parameters

Description

Nyquist plot, i.e., Imaginary part versus Real part of the frequency response of sl.

For continous time systems sl(%i*w) is plotted (w is the frequency in rad/s). For discrete-time systems or discretized systems sl(exp(%i*w*dt)) is used (dt=1 for discrete-time systems and dt=sl('dt') is the sampling period for discretized systems).

sl can be a continuous-time or a 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 or by a row-vector (or a matrix for multi-output) frq.

f_unit selects the desired unit for frequencies: 'h' for Hz or 'r' for rad/s. The default frequency unit is Hz.

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.

Examples

See Also