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Справка Scilab >> CACSD > repfreq


frequency response

Calling Sequence

[ [frq,] repf]=repfreq(sys,fmin,fmax [,step])
[ [frq,] repf]=repfreq(sys [,frq])
[ frq,repf,splitf]=repfreq(sys,fmin,fmax [,step])
[ frq,repf,splitf]=repfreq(sys [,frq])



syslin list : SIMO linear system


two real numbers (lower and upper frequency bounds)


real vector of frequencies (Hz)


logarithmic discretization step


vector of indexes of critical frequencies.


vector of the complex frequency response


repfreq returns the frequency response calculation of a linear system. If sys(s) is the transfer function of Sys, repf(k) equals sys(s) evaluated at s= %i*frq(k)*2*%pi for continuous time systems and at exp(2*%i*%pi*dt*frq(k)) for discrete time systems (dt is the sampling period).

db(k) is the magnitude of repf(k) expressed in dB i.e. db(k)=20*log10(abs(repf(k))) and phi(k) is the phase of repf(k) expressed in degrees.

If fmin,fmax,step are input parameters, the response is calculated for the vector of frequencies frq given by: frq=[10.^((log10(fmin)):step:(log10(fmax))) fmax];

If step is not given, the output parameter frq is calculated by frq=calfrq(sys,fmin,fmax).

Vector frq is split into regular parts with the split vector. frq(splitf(k):splitf(k+1)-1) has no critical frequency. sys has a pole in the range [frq(splitf(k)),frq(splitf(k)+1)] and no poles outside.


frq=0:0.02:5;w=frq*2*%pi; //frq=frequencies in Hz ;w=frequencies in rad/sec;
[frq1,rep] =repfreq(Sys,frq);
Systf=ss2tf(Sys)    //Transfer function of Sys
x=horner(Systf,w(2)*sqrt(-1))    // x is Systf(s) evaluated at s = i w(2)
rep=20*log(abs(x))/log(10)   //magnitude of x in dB
db(2)    // same as rep
ang=atan(imag(x),real(x));   //in rad.
ang=ang*180/%pi              //in degrees

See Also

  • bode — Bode plot
  • freq — frequency response
  • calfrq — frequency response discretization
  • horner — polynomial/rational evaluation
  • nyquist — nyquist plot
  • dbphi — frequency response to phase and magnitude representation
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Last updated:
Thu Oct 02 14:01:06 CEST 2014