filtstates.dfiir (Signal Processing Toolbox)

IIR Direct-form filter states

Syntax

Hs = filtstates.dfiir(numstates,denstates)

Description

Hs = filtstates.dfiir(numstates,denstates) returns an IIR direct-form filter states object Hs with two properties--Numerator and Denominator, which contain the filter states. These two properties are column vectors with each column representing a separate channel of filter states. The number of states is always one less than the the number of filter numerator or denominator coefficients.

You can extract a filtstates object from the states property of an IIR direct-form I object with

```
Hd = dfilt.df1
Hs = Hd.states
```

Methods

You can use the following methods on a filtstates.dfiir object.

Method
Description

double
Converts a filtstates object to a double-precision vector containing the values of the numerator and denominator states. The numerator states are listed first in this vector, followed by the denominator states.

single
Converts a filtstates object to a single-precision vector containing the values of the numerator and denominator states. (This method is used with the Fitler Design Toolbox.)

Method	Description
`double`	Converts a `filtstates` object to a double-precision vector containing the values of the numerator and denominator states. The numerator states are listed first in this vector, followed by the denominator states.
`single`	Converts a `filtstates` object to a single-precision vector containing the values of the numerator and denominator states. (This method is used with the Fitler Design Toolbox.)

Examples

This example demonstrates the interaction of filtstates with a dfilt.df1 object.

[b,a] = butter(4,0.5);       % Design a butterworth filter
Hd = dfilt.df1(b,a);         % Create a dfilt object
Hs = Hd.states               % Extract a filter states object from
                             %  the dfilt states property
Hs.Numerator = [1,1,1,1]'    % Modify the numerator states
Hd.states = Hs               % Set the modified states back to the 
                             %  original object

Dbl = double(Hs)             % Create a double vector from states

filtstates fir1