Matlab's filter function

• The Matlab implementation for the filter is most easily accomplished using the filter function

  y = filter(B, A, x).
  

• The filter function takes three (3) arguments:
  1. feedforward coefficients B,
  2. feedback coefficients A,
  3. and the input signal $x$.

• If the filter doesn't have feedback coefficients, as is the case with an FIR filter, A = 1.

• Our simple low-pass filter, $y(n) = x(n)+x(n-1)$, is a first order filter with 2 feedforward coefficients (B = [1, 1]).

• In matlab:

  B = [1 1];
  A = 1;
  y = filter(B, A, x);