# isreal

Verify that discrete-time filter System object is real

## Syntax

``flag = isreal(sysobj)``

## Description

example

````flag = isreal(sysobj)` determines if the filter coefficients are real. If the filter coefficients are real, `isreal` returns a logical `1`. If the filter coefficients are complex, `isreal` returns a logical `0`. Complex filters have one or more coefficients with nonzero imaginary parts.```

## Examples

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Create a `dsp.SOSFilter` System object™. Pass a fixed-point input to the object. Test the coefficients of the fixed-point filter to see if they are strictly real.

```d = fdesign.lowpass('n,fp,ap,ast',5,0.4,0.5,20); sosFilter = design(d,'ellip',SystemObject=true)```
```sosFilter = dsp.SOSFilter with properties: Structure: 'Direct form II' CoefficientSource: 'Property' Numerator: [3x3 double] Denominator: [3x3 double] HasScaleValues: true ScaleValues: [0.6252 0.5432 0.4861 1] Show all properties ```
`IsRealBefore = isreal(sosFilter)`
```IsRealBefore = logical 1 ```

Pass a fixed-point input to the object.

```fiInput = fi(randn(1000,2),1,32,16); fiOutput = sosFilter(fiInput); IsRealAfter = isreal(sosFilter)```
```IsRealAfter = logical 1 ```

The `isreal` function returns a value of 1, indicating that the filter coefficients are real.

## Output Arguments

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Flag to determine whether the filter coefficients are real, returned as a logical scalar. If the filter coefficients are real, `isreal` returns a logical `1`, else it returns a logical `0`.

Data Types: `logical`

## Version History

Introduced in R2011a