phaseplot

Arguments

sl

A siso or simo linear dynamical system, in state space, transfer function or zpk representations, in continuous or discrete time.

fmin

real scalar: the minimum frequency (in Hz) to be represented.

fmax

real scalar: the maximum frequency (in Hz) to be represented.

step

real scalar: the frequency discretization step (logarithmic scale)). If it is not specified the algorithm uses adaptative frequency steps.

comments

a character string vector: the legend label to be associated with each curve. Optional value is the empty array.

frq

a row vector or an n x m array: The frequency discretization in Hz.

db

an n x m array: the magnitudes corresponding to frq. This argument is not used, it only appears to make phaseplot have the same syntax as gainplot and bode.

phi

an n x m array: the phases in degree corresponding to frq. The phaseplot function plots the curves phi(i,:) versus frq(i,:)

repf

an n x m complex array. The phaseplot function plots the curves phase(repf(i,:)) versus frq(i,:)

Description

This function draws the phase of the frequency response of a system. The system can be given under different representations:

• phaseplot(sl,...) case

  sl can be a continuous-time or discrete-time SIMO system given by its state space, rational transfer function (see syslin) or zpk representation. In case of multi-output the outputs are plotted with different colors.

  In this case the frequencies can be given by:

  • the lower and upper bounds in Hz fmin, fmax and an optional frequency step step. The default values for fmin and fmaxare 1.e-3, 1.e3 if sl is continuous-time or 1.e-3, 0.5/sl.dt (nyquist frequency) if sl is discrete-time. If the step argument is omitted the function use an adaptative frequency step (see calfrq).

  • a row vector or a 2D array frq which gives the frequency values in Hz. 2D array can be used for multi-output systems if one wants to have different frequency discretization for each input/output couple.

• phaseplot(frq,...) case

  This case allows to draw frequency phase plots for previously computed frequency responses. The frequency response can be given either by it's complex representation repf or by it's magnitude phase representation db, phi.

  frq and repf must be row vectors or n x m arrays (each row represent an input/output couple).

The datatips tool may be used to display data along the phase curves.

Examples

s=poly(0,'s')
h1=syslin('c',(s^2+2*0.9*10*s+100)/(s^2+2*0.3*10.1*s+102.01))
h2=syslin('c',(s^2+2*0.1*15.1*s+228.01)/(s^2+2*0.9*15*s+225))
clf();phaseplot([h1;h2],0.01,100,..
                   ["$\frac{s^2+18 s+100}{s^2+6.06 s+102.1}$";
                    "$\frac{s^2+3.02 s+228.01}{s^2+27 s+225}$"])
title('Phaseplot')

See also

• bode — Bode plot
• gainplot — magnitude plot
• repfreq — frequency response
• calfrq — frequency response discretization
• datatips — Tool for placing and editing tips along the plotted curves.

History