Documentation

# ismaxphase

Determine whether filter is maximum phase

## Syntax

```flag = ismaxphase(b,a) flag = ismaxphase(sos) flag = ismaxphase(d) flag = ismaxphase(...,tol) flag = ismaxphase(hs,...) flag = ismaxphase(hs,'Arithmetic',arithtype) ```

## Description

`flag = ismaxphase(b,a)` returns a logical output, `flag`, equal to `true` if the filter specified by numerator coefficients, `b`, and denominator coefficients, `a`, is a maximum phase filter.

`flag = ismaxphase(sos)` returns `true` if the filter specified by second order sections matrix, `sos`, is a maximum phase filter. `sos` is a K-by-6 matrix, where the number of sections, K, must be greater than or equal to 2. Each row of `sos` corresponds to the coefficients of a second order (biquad) filter. The ith row of the `sos` matrix corresponds to ```[bi(1) bi(2) bi(3) ai(1) ai(2) ai(3)]```.

`flag = ismaxphase(d)` returns `true` if the digital filter, `d`, has maximum phase. Use `designfilt` to generate `d` based on frequency-response specifications.

`flag = ismaxphase(...,tol)` uses the tolerance, `tol`, to determine when two numbers are close enough to be considered equal. If not specified, `tol`, defaults to `eps^(2/3)`.

```flag = ismaxphase(hs,...)``` returns `true`if the filter System object™ `hs` is a maximum phase filter. You must have the DSP System Toolbox™ software to use this syntax.

```flag = ismaxphase(hs,'Arithmetic',arithtype)``` analyzes the filter System object `hs` based on the specified `arithtype`. `arithtype` can be `'double'`, `'single'`, or `'fixed'`. When you specify `'double'` or `'single'`, the function performs double- or single-precision analysis. When you specify `'fixed'` , the arithmetic changes depending on the setting of the `CoefficientDataType` property and whether the System object is locked or unlocked. You must have the DSP System Toolbox software to use this syntax.

When you do not specify the arithmetic for non-CIC structures, the function uses double-precision arithmetic if the filter System object is in an unlocked state. If the System object is locked, the function performs analysis based on the locked input data type. CIC structures only support fixed-point arithmetic.

## Examples

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Design maximum-phase and minimum-phase lattice filters and verify their phase type.

```k = [1/6 1/1.4]; bmax = latc2tf(k,'max'); bmin = latc2tf(k,'min'); max_flag = ismaxphase(bmax)```
```max_flag = logical 1 ```
`min_flag = isminphase(bmin)`
```min_flag = logical 1 ```

Given a filter defined with a set of single precision numerator and denominator coefficients, check if it is maximum phase for different values of the tolerance.

```b = single([1 -0.9999]); a = single([1 0.45]); max_flag1 = ismaxphase(b,a)```
```max_flag1 = logical 0 ```
`max_flag2 = ismaxphase(b,a,1e-3)`
```max_flag2 = logical 1 ```

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