# Documentation

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# isfir

Determine if digital filter has finite impulse response

## Syntax

``````flag = isfir(d)``````

## Description

example

``````flag = isfir(d)``` returns `true` if a digital filter, `d`, has a finite impulse response.```

## Examples

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Use `designfilt` to design FIR and IIR versions of a highpass filter. Specify a normalized stopband frequency of 0.3 and a normalized passband frequency of 0.6. Verify that each filter is of the correct class. Display the frequency responses of the filters.

```fir = designfilt('highpassfir','StopbandFrequency',0.3,'PassbandFrequency',0.6); iir = designfilt('highpassiir','StopbandFrequency',0.3,'PassbandFrequency',0.6); isfirFIR = isfir(fir)```
```isfirFIR = logical 1 ```
`isiirFIR = isfir(iir)`
```isiirFIR = logical 0 ```
```fvt = fvtool(fir,iir); legend(fvt,'FIR','IIR')```

## Input Arguments

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Digital filter, specified as a `digitalFilter` object. Use `designfilt` to generate a digital filter based on frequency-response specifications.

Example: `d = designfilt('lowpassiir','FilterOrder',3,'HalfPowerFrequency',0.5)` specifies a third-order Butterworth filter with normalized 3-dB frequency 0.5π rad/sample.

## Output Arguments

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Filter class identification, returned as a logical scalar.