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# igamax

> Find the index of the first element having the maximum absolute value.

<section class="usage">

## Usage

```javascript
var igamax = require( '@stdlib/blas/base/igamax' );
```

#### igamax( N, x, strideX )

Finds the index of the first element having the maximum absolute value.

```javascript
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

var idx = igamax( x.length, x, 1 );
// returns 3
```

The function has the following parameters:

-   **N**: number of indexed elements.
-   **x**: input array.
-   **strideX**: stride length for `x`.

The `N` and stride parameters determine which elements in the strided array are accessed at runtime. For example, to traverse every other value,

```javascript
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

var idx = igamax( 4, x, 2 );
// returns 2
```

Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.

```javascript
var Float64Array = require( '@stdlib/array/float64' );

// Initial array:
var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );

// Create an offset view:
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

// Find index of element having the maximum absolute value:
var idx = igamax( 3, x1, 2 );
// returns 2
```

#### igamax.ndarray( N, x, strideX, offset )

Finds the index of the first element having the maximum absolute value using alternative indexing semantics.

```javascript
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

var idx = igamax.ndarray( x.length, x, 1, 0 );
// returns 3
```

The function has the following additional parameters:

-   **offsetX**: starting index.

While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying buffer, the offset parameter supports indexing semantics based on a starting index. For example, to start from the second index,

```javascript
var x = [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ];

var idx = igamax.ndarray( 5, x, 1, 1 );
// returns 4
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   If `N < 1`, both functions return `-1`.
-   `igamax()` corresponds to the [BLAS][blas] level 1 function [`idamax`][idamax] with the exception that this implementation works with any array type, not just Float64Arrays. Depending on the environment, the typed versions ([`idamax`][@stdlib/blas/base/idamax], [`isamax`][@stdlib/blas/base/isamax], etc.) are likely to be significantly more performant.
-   Both functions support array-like objects having getter and setter accessors for array element access (e.g., [`@stdlib/array/base/accessor`][@stdlib/array/base/accessor]).

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var igamax = require( '@stdlib/blas/base/igamax' );

var opts = {
    'dtype': 'generic'
};
var x = discreteUniform( 10, -100, 100, opts );
console.log( x );

var idx = igamax( x.length, x, 1 );
console.log( idx );
```

</section>

<!-- /.examples -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="links">

[blas]: http://www.netlib.org/blas

[idamax]: https://www.netlib.org/lapack/explore-html/dd/d52/group__iamax_gacec03c5109f531c06b4fb301cf1a2d7a.html

[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray

[@stdlib/blas/base/idamax]: https://github.com/stdlib-js/blas/tree/main/base/idamax

[@stdlib/blas/base/isamax]: https://github.com/stdlib-js/blas/tree/main/base/isamax

[@stdlib/array/base/accessor]: https://www.npmjs.com/package/@stdlib/array-base-accessor

</section>

<!-- /.links -->
