## Name

group — group delay for digital filter

## Calling Sequence

[tg,fr]=group(npts,a1i,a2i,b1i,b2i)

## Parameters

- npts
integer : number of points desired in calculation of group delay

- a1i
in coefficient, polynomial, rational polynomial, or cascade polynomial form this variable is the transfer function of the filter. In coefficient polynomial form this is a vector of coefficients (see below).

- a2i
in coeff poly form this is a vector of coeffs

- b1i
in coeff poly form this is a vector of coeffs

- b2i
in coeff poly form this is a vector of coeffs

- tg
values of group delay evaluated on the grid fr

- fr
grid of frequency values where group delay is evaluated

## Description

Calculate the group delay of a digital filter
with transfer function h(z).

The filter specification can be in coefficient form,
polynomial form, rational polynomial form, cascade
polynomial form, or in coefficient polynomial form.

In the coefficient polynomial form the transfer function is
formulated by the following expression

`h(z)=prod(a1i+a2i*z+z**2)/prod(b1i+b2i*z+z^2)`

## Examples

z=poly(0,'z');
h=z/(z-.5);
[tg,fr]=group(100,h);
plot(fr,tg)