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feat: add blas/base/igamax
PR-URL: #7287 Ref: #2039 Co-authored-by: Athan Reines <[email protected]> Reviewed-by: Athan Reines <[email protected]> Co-authored-by: stdlib-bot <[email protected]>
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‎lib/node_modules/@stdlib/blas/base/igamax/README.md

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<!--
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@license Apache-2.0
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Copyright (c) 2025 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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# igamax
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> Find the index of the first element having the maximum absolute value.
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<section class="usage">
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## Usage
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```javascript
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var igamax = require( '@stdlib/blas/base/igamax' );
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```
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#### igamax( N, x, strideX )
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Finds the index of the first element having the maximum absolute value.
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```javascript
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var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
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var idx = igamax( x.length, x, 1 );
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// returns 3
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```
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The function has the following parameters:
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- **N**: number of indexed elements.
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- **x**: input array.
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- **strideX**: stride length for `x`.
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The `N` and stride parameters determine which elements in the strided array are accessed at runtime. For example, to traverse every other value,
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```javascript
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var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
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var idx = igamax( 4, x, 2 );
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// returns 2
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```
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Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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// Initial array:
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var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
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// Create an offset view:
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var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
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// Find index of element having the maximum absolute value:
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var idx = igamax( 3, x1, 2 );
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// returns 2
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```
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#### igamax.ndarray( N, x, strideX, offset )
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Finds the index of the first element having the maximum absolute value using alternative indexing semantics.
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```javascript
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var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
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var idx = igamax.ndarray( x.length, x, 1, 0 );
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// returns 3
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```
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The function has the following additional parameters:
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- **offsetX**: starting index.
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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,
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```javascript
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var x = [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ];
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var idx = igamax.ndarray( 5, x, 1, 1 );
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// returns 4
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- If `N < 1`, both functions return `-1`.
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- `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.
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- 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]).
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</section>
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<!-- /.notes -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
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var igamax = require( '@stdlib/blas/base/igamax' );
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var opts = {
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'dtype': 'generic'
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};
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var x = discreteUniform( 10, -100, 100, opts );
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console.log( x );
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var idx = igamax( x.length, x, 1 );
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console.log( idx );
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```
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</section>
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<!-- /.examples -->
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<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
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<section class="related">
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</section>
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<!-- /.related -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="links">
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[blas]: http://www.netlib.org/blas
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[idamax]: https://netlib.org/lapack/explore-html-3.6.1/dd/de0/idamax_8f_a285793254ff0adaf58c605682efb880c.html
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[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
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[@stdlib/blas/base/idamax]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/blas/base/idamax
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[@stdlib/blas/base/isamax]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/blas/base/isamax
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[@stdlib/array/base/accessor]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/base/accessor
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/blas/base/igamax/benchmark/benchmark.js

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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2025 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var bench = require( '@stdlib/bench' );
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var uniform = require( '@stdlib/random/array/uniform' );
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var isnan = require( '@stdlib/math/base/assert/is-nan' );
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var pow = require( '@stdlib/math/base/special/pow' );
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var pkg = require( './../package.json' ).name;
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var igamax = require( './../lib' );
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// VARIABLES //
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var options = {
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'dtype': 'float64'
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};
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// FUNCTIONS //
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/**
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* Create a benchmark function.
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*
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* @private
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* @param {PositiveInteger} len - array length
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* @returns {Function} benchmark function
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*/
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function createBenchmark( len ) {
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var x = uniform( len, -100.0, 100.0, options );
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return benchmark;
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function benchmark( b ) {
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var idx;
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var i;
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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idx = igamax( x.length, x, 1 );
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if ( isnan( idx ) ) {
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b.fail( 'should not return NaN' );
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}
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}
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b.toc();
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if ( isnan( idx ) ) {
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b.fail( 'should not return NaN' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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}
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}
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// MAIN //
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function main() {
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var len;
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var min;
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var max;
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var f;
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var i;
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min = 1; // 10^min
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max = 6; // 10^max
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for ( i = min; i <= max; i++ ) {
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len = pow( 10, i );
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f = createBenchmark( len );
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bench( pkg+':len='+len, f );
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}
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}
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main();

‎lib/node_modules/@stdlib/blas/base/igamax/benchmark/benchmark.ndarray.js

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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2025 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var bench = require( '@stdlib/bench' );
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var uniform = require( '@stdlib/random/array/uniform' );
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var isnan = require( '@stdlib/math/base/assert/is-nan' );
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var pow = require( '@stdlib/math/base/special/pow' );
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var pkg = require( './../package.json' ).name;
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var igamax = require( './../lib' ).ndarray;
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// VARIABLES //
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var options = {
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'dtype': 'float64'
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};
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// FUNCTIONS //
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/**
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* Create a benchmark function.
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*
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* @private
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* @param {PositiveInteger} len - array length
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* @returns {Function} benchmark function
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*/
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function createBenchmark( len ) {
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var x = uniform( len, -100.0, 100.0, options );
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return benchmark;
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function benchmark( b ) {
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var idx;
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var i;
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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idx = igamax( x.length, x, 1, 0 );
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if ( isnan( idx ) ) {
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b.fail( 'should not return NaN' );
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}
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}
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b.toc();
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if ( isnan( idx ) ) {
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b.fail( 'should not return NaN' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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}
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}
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// MAIN //
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function main() {
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var len;
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var min;
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var max;
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var f;
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var i;
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min = 1; // 10^min
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max = 6; // 10^max
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for ( i = min; i <= max; i++ ) {
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len = pow( 10, i );
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f = createBenchmark( len );
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bench( pkg+':ndarray:len='+len, f );
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}
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}
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main();

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