igamax

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

Installation

npm install @stdlib/blas-base-igamax

Usage

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

igamax( N, x, strideX )

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

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,

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 views.

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.

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 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,

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

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

Notes

• If N < 1, both functions return -1.
• igamax() corresponds to the BLAS level 1 function idamax with the exception that this implementation works with any array type, not just Float64Arrays. Depending on the environment, the typed versions (idamax, 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).

Examples

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 );

Notice

This package is part of 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, see the main project repository.

Community

License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.