# tf

Transfer function

## Syntax

``[B,A] = tf(npFilter)``
``[B,A,B2,A2] = tf(npFilter)``

## Description

````[B,A] = tf(npFilter)` returns the vector of numerator coefficients, `B`, and the vector of denominators, `A`, for the equivalent transfer function corresponding to the notch filter.```

example

````[B,A,B2,A2] = tf(npFilter)` also returns the vector of numerator coefficients, `B2`, and the vector of denominator coefficients, `A2`, for the equivalent transfer function corresponding to the peak filter.```

## Examples

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Create a `dsp.NotchPeakFilter` System object™. Obtain the coefficients of the transfer function corresponding to the notch and peak filters.

```notchpeak = dsp.NotchPeakFilter; [Bnotch,Anotch,Bpeak,Apeak] = tf(notchpeak)```
```Bnotch = 1×3 0.8633 -0.0000 0.8633 ```
```Anotch = 1×3 1.0000 -0.0000 0.7265 ```
```Bpeak = 1×3 0.1367 0 -0.1367 ```
```Apeak = 1×3 1.0000 -0.0000 0.7265 ```

`Bnotch` and `Anotch` are the vectors of numerator and denominator coefficients for the equivalent transfer function corresponding to the notch filter. `Bpeak` and `Apeak` are the vectors of numerator and denominator coefficients for the equivalent transfer function corresponding to the peak filter.

## Input Arguments

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Notch peak filter object, specified as a `dsp.NotchPeakFilter` object.

## Output Arguments

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Numerator coefficients for the equivalent transfer function corresponding to the notch filter, specified as a vector.

Data Types: `double`

Denominator coefficients for the equivalent transfer function corresponding to the notch filter, specified as a vector.

Data Types: `double`

Numerator coefficients for the equivalent transfer function corresponding to the peak filter, specified as a vector.

Data Types: `double`

Denominator coefficients for the equivalent transfer function corresponding to the peak filter, specified as a vector.

Data Types: `double`

## Version History

Introduced in R2014a