SFREQ

Purpose:

Evaluates the frequency response of a Laplace transform in Hertz.

Syntax:

SFREQ(b, a, N)

(h, f) = SFREQ(b, a, N)

b

-

A series. The numerator (i.e. zero) coefficients.

a

-

A series. The denominator (i.e. pole) coefficients.

N

-

Optional. An integer, the number of output samples, defaults to 200.

Alternate Syntax:

 

SFREQ(b, a, f)

(h, f) = SFREQ(b, a, f)

b

-

A series. The numerator (i.e. zero) coefficients.

a

-

A series. The denominator (i.e. pole) coefficients.

f

-

A series. The frequencies in Hertz to evaluate the system.

Returns:

Displays the magnitude and phase response in two Windows.

h = SFREQ(b, a) returns the complex frequency response as one XY series.

(h, f) = SFREQ(b, a) returns the complex frequency response as two separate series.

Example:

h = sfreq({1000}, {1, 5, 2000})

 

h contains 200 samples of the frequency response of the continuous system:

 

image\sfreq01.gif

 

The frequency values range from 0 to 15.92 Hertz.

Example:

freqs({1000}, {1, 5, 2000}, 1024)

 

Returns 1024 samples of the magnitude and phase response of the system in two separate Windows:

Example:

b = {0.2, 0.3, 1.0}

a = {1.0, 0.4, 1.0}

f = logspace(-2, 1)

sfreq(b, a, f)

 

image\sfreqpic.gif

 

Displays 100 samples of the magnitude and phase response of the system:

 

image\freqs02.gif

 

The frequency values range from 0.01 Hertz to 10 Hertz.

Remarks:

SFREQ displays the magnitude and phase response of the continuous system specified by the Laplace transform:

 

image\res06.gif

 

s

=

complex frequency

N

=

number of numerator terms

M

=

number of denominator terms

 

If no output arguments are provided, the magnitude and phase response are displayed in two separate windows.

 

The frequency values f, are in Hertz where:

 

f = ω / 2π

 

See FREQS to display a continuous complex frequency response with angular frequency values in radians/s.

 

SFREQ(b, a) or SFREQ(b, a, N) automatically chooses frequencies to best capture the magnitude characteristics of the system

 

SFREQ(b, a, f) where f is a series, computes the frequency response at each frequency sample of f.

See Also:

FILTEQ

FREQS

FREQZ

IMPS

INVFREQS

INVFREQZ

MAGNITUDE

PHASE

RESIDUE

RESIDUEZ

SPLANE

ZFREQ