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# iterHannPulse

> Create an iterator which generates a Hann pulse waveform.

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<section class="intro">

A Hann pulse waveform is represented by the following equation

<!-- <equation class="equation" label="eq:hann_pulse_waveform" align="center" raw="f(t; T, \tau, a, \varphi) = \begin{cases} \frac{a}{2}\biggl(1-\cos \frac{2\pi (t-\varphi)}{\tau-1}\biggr) & (t-\varphi) \mod T < \tau \\ 0 & \textrm{otherwise} \end{cases}" alt="Equation for a Hann pulse waveform."> -->

<div class="equation" align="center" data-raw-text="f(t; T, \tau, a, \varphi) = \begin{cases} \frac{a}{2}\biggl(1-\cos \frac{2\pi (t-\varphi)}{\tau-1}\biggr) &amp; (t-\varphi) \mod T < \tau \\ 0 &amp; \textrm{otherwise} \end{cases}" data-equation="eq:hann_pulse_waveform">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@08cee6de617d64ec3324479142e1cdf0036898d8/lib/node_modules/@stdlib/simulate/iter/hann-pulse/docs/img/equation_hann_pulse_waveform.svg" alt="Equation for a Hann pulse waveform.">
    <br>
</div>

<!-- </equation> -->

where `T` is the pulse period, `τ` is the pulse duration, `a` is the amplitude, and `φ` is the phase offset.

<!-- TODO: add a figure showing a Hann pulse train -->

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="usage">

## Usage

```javascript
var iterHannPulse = require( '@stdlib/simulate/iter/hann-pulse' );
```

#### iterHannPulse( \[options] )

Returns an iterator which generates a Hann pulse waveform.

```javascript
var it = iterHannPulse();
// returns <Object>

var v = it.next().value;
// returns <number>

v = it.next().value;
// returns <number>

v = it.next().value;
// returns <number>

// ...
```

The returned iterator protocol-compliant object has the following properties:

-   **next**: function which returns an iterator protocol-compliant object containing the next iterated value (if one exists) assigned to a `value` property and a `done` property having a `boolean` value indicating whether the iterator is finished.
-   **return**: function which closes an iterator and returns a single (optional) argument in an iterator protocol-compliant object.

The function supports the following `options`:

-   **period**: pulse period (i.e., the number of iterations before a waveform repeats). Default: `100`.
-   **duration**: pulse duration. Must be greater than `2`. Default: `options.period`.
-   **amplitude**: amplitude. Default: `1.0`.
-   **offset**: phase offset (in units of iterations; zero-based). A negative offset translates a waveform to the left. A positive offset translates a waveform to the right. Default: `0`.
-   **iter**: number of iterations. Default: `1e308`.

By default, the function returns an iterator which generates a waveform that repeats every `100` iterations. To specify an alternative period, set the `period` option.

```javascript
var opts = {
    'period': 10
};

var it = iterHannPulse( opts );
// returns <Object>

var v = it.next().value;
// returns <number>

v = it.next().value;
// returns <number>

// ...
```

By default, the function returns an iterator which generates a waveform that has a duty cycle of `100%` (i.e., the waveform duration equals the waveform period). To specify an alternative duty cycle, set the `duration` option. For example, to generate a waveform having a period of `10` iterations and a `50%` duty cycle,

```javascript
var opts = {
    'period': 10,
    'duration': 5 // 5/10 = 0.50 => 50%
};

var it = iterHannPulse( opts );
// returns <Object>

var v = it.next().value;
// returns 0.0

v = it.next().value;
// returns <number>

v = it.next().value;
// returns <number>

v = it.next().value;
// returns <number>

v = it.next().value;
// returns 0.0

v = it.next().value;
// returns 0.0

v = it.next().value;
// returns 0.0

v = it.next().value;
// returns 0.0

v = it.next().value;
// returns 0.0

v = it.next().value;
// returns 0.0

// ...
```

To adjust at what point the iterator begins in the waveform cycle, set the phase `offset` option. For example, to translate the waveform to the left,

```javascript
var opts = {
    'period': 10,
    'duration': 5,
    'offset': -7
};

var it = iterHannPulse( opts );
// returns <Object>

var v = it.next().value;
// returns 0.0

v = it.next().value;
// returns 0.0

v = it.next().value;
// returns 0.0

v = it.next().value;
// returns 0.0

v = it.next().value;
// returns <number>

v = it.next().value;
// returns <number>

// ...
```

To translate the waveform to the right,

```javascript
var opts = {
    'period': 10,
    'duration': 5,
    'offset': 2
};

var it = iterHannPulse( opts );
// returns <Object>

var v = it.next().value;
// returns 0.0

v = it.next().value;
// returns 0.0

v = it.next().value;
// returns 0.0

v = it.next().value;
// returns <number>

v = it.next().value;
// returns <number>

// ...
```

By default, the function returns an infinite iterator (i.e., an iterator which never ends). To limit the number of iterations, set the `iter` option.

```javascript
var opts = {
    'iter': 2
};
var it = iterHannPulse( opts );
// returns <Object>

var v = it.next().value;
// returns <number>

v = it.next().value;
// returns <number>

var bool = it.next().done;
// returns true
```

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## Notes

-   If an environment supports `Symbol.iterator`, the returned iterator is iterable.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var iterHannPulse = require( '@stdlib/simulate/iter/hann-pulse' );

// Create an iterator:
var opts = {
    'period': 50,
    'duration': 25,
    'amplitude': 10.0,
    'offset': -25,
    'iter': 100
};
var it = iterHannPulse( opts );

// Perform manual iteration...
var v;
while ( true ) {
    v = it.next();
    if ( v.done ) {
        break;
    }
    console.log( v.value );
}
```

</section>

<!-- /.examples -->

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<section class="references">

</section>

<!-- /.references -->

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</section>

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