npm package: @stdlib/blas-base-igamax
Description: Find the index of the first element having the maximum absolute value.
Author: The Stdlib Authors
Latest version: 0.1.1

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# igamax

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

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

<section class="installation">

## Installation

```bash
npm install @stdlib/blas-base-igamax
```

</section>

<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 -->

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<section class="main-repo" >

* * *

## Notice

This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].

#### Community

[![Chat][chat-image]][chat-url]

---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

</section>

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[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules

[deno-url]: https://github.com/stdlib-js/blas-base-igamax/tree/deno
[deno-readme]: https://github.com/stdlib-js/blas-base-igamax/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/blas-base-igamax/tree/umd
[umd-readme]: https://github.com/stdlib-js/blas-base-igamax/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/blas-base-igamax/tree/esm
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[branches-url]: https://github.com/stdlib-js/blas-base-igamax/blob/main/branches.md

[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/blas-base-igamax/main/LICENSE

[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://www.npmjs.com/package/@stdlib/blas-base-idamax

[@stdlib/blas/base/isamax]: https://www.npmjs.com/package/@stdlib/blas-base-isamax

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

</section>

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