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Reference Guide for OpenMatrix Language Functions
The Reference Guide contains documentation for all functions supported in the OpenMatrix language.
Signal Processing Commands
buttap
Create a normalized Butterworth analog lowpass prototype filter in zero-pole-gain form.

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- Extended Definitions for Advanced Users
  PDF file with in-depth information on key topics in the User's Guide.
- Scripting Guide for OpenMatrix Language
  OpenMatrix is a mathematical scripting language.
- Reference Guide for OpenMatrix Language Functions
  The Reference Guide contains documentation for all functions supported in the OpenMatrix language.
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  - Signal Processing Commands
    - barthannwin
      Bartlett-Hann window.
    - bessel3ap
      Create a normalized Bessel analog lowpass prototype filter in zero-pole-gain form.
    - besselap
      Create a normalized Bessel analog lowpass prototype filter in zero-pole-gain form.
    - besself
      Create a Bessel filter.
    - besself3
      Create a Bessel filter.
    - blackman
      Blackman window.
    - buttap
      Create a normalized Butterworth analog lowpass prototype filter in zero-pole-gain form.
    - butter
      Create a Butterworth filter.
    - buttord
      Design a Butterworth filter.
    - cheb1ap
      Create a normalized Chebyshev I analog lowpass prototype filter in zero-pole-gain form.
    - cheb2ap
      Create a normalized Chebyshev II analog lowpass prototype filter in zero-pole-gain form.
    - cheb1ord
      Design a Chebyshev I filter.
    - cheb2ord
      Design a Chebyshev II filter.
    - chebwin
      Dolph-Chebyshev window.
    - cheby1
      Create a Chebyshev I filter.
    - cheby2
      Create a Chebyshev II filter.
    - chirp
      Generate a chirp signal.
    - cmorwavf
      Generate a complex Morlet wavelet.
    - cpsd
      Compute cross power spectral density.
    - downsample
      Downsample a signal.
    - dba
      Acoustic A-weighting function.
    - dbb
      Acoustic B-weighting function.
    - dbc
      Acoustic C-weighting function.
    - dbu
      Acoustic U-weighting function.
    - diric
      Generate the Dirichlet function.
    - ellip
      Create an Elliptic filter.
    - ellipap
      Create a normalized Elliptic analog lowpass prototype filter in zero-pole-gain form.
    - ellipord
      Design an Elliptic filter.
    - fft
      Fast Fourier Transform.
    - fft2
      Two Dimensional Fast Fourier Transform.
    - fftn
      N dimensional fast Fourier transform (FFT).
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      Shift frequency spectrum related vectors to center the dc element
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      Filter a signal with an IIR or FIR filter.
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      Perform 2D FIR filtering.
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      Filter a signal forward and then backward, compensating for end effects.
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      Locate the peaks of a signal.
    - fir1
      Create a digital FIR filter.
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      Create a digital FIR multi-band filter with a least squares fitting.
    - fold
      Create one-sided spectrum amplitude vectors from the two-sided equivalents.
    - freq
      Generate a vector of frequency locations.
    - freqs
      Compute analog filter frequency response values.
    - freqz
      Compute digital filter frequency response values.
    - gauspuls
      Generate a sampled Gaussian modulated sinusoidal pulse centered at zero, with a specified center frequency and fractional bandwidth.
    - gmonopuls
      Generate a sampled Gaussian monopulse.
    - grpdelay
      Compute digital filter group delay values.
    - hamming
      Hamming window.
    - hann
      Hann window.
    - hilbert
      Hilbert transform.
    - ifft
      Inverse Fast Fourier transform.
    - ifft2
      Two-dimensional inverse fast Fourier transform.
    - ifftn
      N dimensional inverse fast Fourier transform.
    - ifftshift
      Shift frequency spectrum related vectors to uncenter the dc element to the first position.
    - impz
      Compute the impulse response of a digital filter.
    - invfreqs
      Compute analog filter coefficients from frequency response values.
    - invfreqz
      Compute digital filter coefficients from frequency response values.
    - istft
      Inverse Short-Time Fourier Transform.
    - kaiser
      Kaiser-Bessel window.
    - medfilt1
      Applies a moving median filter in one dimension.
    - mexihat
      Generate a Mexican hat wavelet.
    - meyeraux
      Generate a Meyer auxiliary wavelet.
    - mscohere
      Estimates the mean squared coherence of time domain signals.
    - morlet
      Generate a Morlet wavelet.
    - parzenwin
      Parzen window.
    - peak2peak
      Compute signal maximum to minimum differences.
    - peak2rms
      Compute signal peak to rms ratios.
    - pulstran
      Generate a pulse train, with the pulse defined either by a function or a sampled pulse.
    - pwelch
      Computes the power spectral density.
    - rectpuls
      Generate a sampled rectangular pulse centered at zero, with a specified width.
    - resample
      Resample a real signal by a rational factor using a polyphase FIR filter.
    - rssq
      Compute root sum squared values.
    - sawtooth
      Generate a sawtooth wave with range [-1,1] and period 2*pi.
    - shanwavf
      Generate a complex Shannon wavelet.
    - shiftdata
      Transfer a designated matrix dimension to the lead position.
    - sosfilt
      Filter a real signal with a second order section IIR filter.
    - square
      Generate a square wave with range [-1,1] and period 2*pi.
    - sinc
      Compute the sinc function.
    - stft
      Short-Time Fourier Transform.
    - spectrogram
      Spectrogram.
    - stairs
      Generate a stair step plot.
    - tfestimate
      Estimates the transfer function from time domain signals.
    - tripuls
      Generate a sampled triangular pulse centered at zero, with a specified width and skew.
    - udecode
      Convert quantized integer matrix elements to floating-point values.
    - uencode
      Quantize real matrix elements to integer values.
    - unshiftdata
      Revert the order of matrix dimensions modified by shiftdata.
    - unwrap
      Unwrap a vector of phase angles.
    - upsample
      Upsample a signal.
    - welchwin
      Welch window.
    - xcorr
      Cross correlation, computed over a range of lags.
    - xcov
      Cross covariance, computed over a range of lags.
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- Function Guide for Twin Activate
  Provides information about developing and simulating models through the Twin Activate Application Program Interface.
- Glossary
  Key terms associated with the software.
Frequently Asked Questions
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buttap

Create a normalized Butterworth analog lowpass prototype filter in zero-pole-gain form.

Syntax

[z,p,k] = buttap(n)

Inputs

n: The filter order.; Type: integer; Dimension: scalar

Outputs

z: The zeros of the filter.; Type: vector
p: The poles of the filter.; Type: vector
k: The gain factor.; Type: scalar

Examples

Create a fourth order Butterworth analog prototype filter.

[z,p,k] = buttap(4)

z = [Matrix] 0 x 1
p = [Matrix] 4 x 1
-0.38268 + 0.92388i
-0.92388 + 0.38268i
-0.92388 - 0.38268i
-0.38268 - 0.92388i
k = 1

Comments

The Butterworth prototype has -3dB attenuation at a 1 radian/sec cutoff frequency. Analog Butterworth filters have no zeros.