Communications Toolbox

filter

One-dimensional digital filter over a Galois field

Syntax

• y = filter(b,a,x);
  [y,zf] = filter(b,a,x);
  

Description

y = filter(b,a,x) filters the data in the vector x with the filter described by numerator coefficient vector b and denominator coefficient vector a. The vectors b, a, and x must be Galois vectors in the same field. If a(1) is not equal to 1, then filter normalizes the filter coefficients by a(1). As a result, a(1) must be nonzero.

The filter is a "Direct Form II Transposed" implementation of the standard difference equation below.

• a(1)*y(n) = b(1)*x(n) + b(2)*x(n-1) + ... + b(nb+1)*x(n-nb) ...
                        - a(2)*y(n-1) - ... - a(na+1)*y(n-na)
  

[y,zf] = filter(b,a,x) returns the final conditions of the filter delays in the Galois vector zf. The length of the vector zf is max(size(a),size(b))-1.

Examples

An example is in Filtering.

fft

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