Signal Processing Toolbox

eqtflength

Make the lengths of a transfer function's numerator and denominator equal

Syntax

• [b,a] = eqtflength(num,den)
  [b,a,n,m] = eqtflength(num,den)
  

Description

[b,a] = eqtflength(num,den) modifies the vector num and/or the vector den, so that the resulting output vectors b and a have the same length. The input vectors num and den may have different lengths. The vector num represents the numerator polynomial of a given discrete-time transfer function, and the vector den represents its denominator. The resulting numerator b and denominator a represent the same discrete-time transfer function, but these vectors have the same length.

[b,a,n,m] = eqtflength(num,den) modifies the vectors as above and also returns the numerator order n and the denominator m, not including any trailing zeros.

Use eqtflength to obtain a numerator and denominator of equal length before applying transfer function conversion functions such as tf2ss and tf2zp to discrete-time models.

Examples

• num = [1 0.5];
  den = [1 0.75 0.6 0];
  [b,a,n,m] = eqtflength(num,den)
  b =
      1.0000    0.5000         0
  a =
      1.0000    0.7500    0.6000
  n =
       1
  m =
       2
  

Algorithm

eqtflength(num,den) appends zeros to either num or den as necessary. If both num and den have trailing zeros in common, these are removed.

See Also

tf2ss, tf2zp

ellipord

fdatool