feat: add blas/base/izamax

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Jan 17, 2025 · Jan 17, 2025 · Jun 13, 2025 · Jan 17, 2025 · 10285d405f011c35305358e28e07dd32fbe0d7cf
commit 10285d405f011c35305358e28e07dd32fbe0d7cf
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+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2025 The Stdlib Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+-->
+
+# izamax
+
+> Find the index of the first element having the maximum absolute value.
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var izamax = require( '@stdlib/blas/base/izamax' );
+```
+
+#### izamax( N, zx, strideX )
+
+Finds the index of the first element having the maximum absolute value.
+
+```javascript
+var Complex128Array = require( '@stdlib/array/complex128' );
+
+var zx = new Complex128Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
+
+var idx = izamax( zx.length, zx, 1 );
+// returns 1
+```
+
+The function has the following parameters:
+
+- **N**: number of indexed elements.
+- **zx**: input [`Complex128Array`][@stdlib/array/complex128].
+- **strideX**: index increment for `zx`.
+
+The `N` and `strideX` parameters determine which elements in `zx` are accessed at runtime. For example, to traverse every other value,
+
+```javascript
+var Complex128Array = require( '@stdlib/array/complex128' );
+
+var zx = new Complex128Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
+
+var idx = izamax( 2, zx, 2 );
+// returns 1
+```
+
+Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
+
+```javascript
+var Complex128Array = require( '@stdlib/array/complex128' );
+
+// Initial array:
+var zx0 = new Complex128Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
+
+// Create an offset view:
+var zx1 = new Complex128Array( zx0.buffer, zx0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
+
+// Find index of element having the maximum absolute value:
+var idx = izamax( 2, zx1, 1 );
+// returns 1
+```
+
+#### izamax.ndarray( N, zx, strideX, offset )
+
+Finds the index of the first element having the maximum absolute value using alternative indexing semantics.
+
+```javascript
+var Complex128Array = require( '@stdlib/array/complex128' );
+
+var zx = new Complex128Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
+
+var idx = izamax.ndarray( zx.length, zx, 1, 0 );
+// returns 1
+```
+
+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 Complex128Array = require( '@stdlib/array/complex128' );
+
+var zx = new Complex128Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0, 7.0, -8.0 ] );
+
+var idx = izamax.ndarray( 3, zx, 1, 1 );
+// returns 2
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="notes">
+
+## Notes
+
+- If `N < 1`, both functions return `-1`.
+- `izamax()` corresponds to the [BLAS][blas] level 1 function [`izamax`][izamax].
+
+</section>
+
+<!-- /.notes -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
+var filledarrayBy = require( '@stdlib/array/filled-by' );
+var Complex128 = require( '@stdlib/complex/float64/ctor' );
+var izamax = require( '@stdlib/blas/base/izamax' );
+
+function rand() {
+return new Complex128( discreteUniform( 0, 10 ), discreteUniform( -5, 5 ) );
+}
+
+// Generate random input arrays:
+var zx = filledarrayBy( 10, 'complex128', rand );
+console.log( zx.toString() );
+
+var idx = izamax( zx.length, zx, 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
+
+[izamax]: https://netlib.org/lapack/explore-html/d0/da5/izamax_8f.html
+
+[@stdlib/array/complex128]: https://.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/complex128
+
+[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
+
+</section>
+
+<!-- /.links -->
@@ -0,0 +1,105 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2025 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var bench = require( '@stdlib/bench' );
+var uniform = require( '@stdlib/random/array/uniform' );
+var isnan = require( '@stdlib/math/base/assert/is-nan' );
+var pow = require( '@stdlib/math/base/special/pow' );
+var Complex128Array = require( '@stdlib/array/complex128' );
+var pkg = require( './../package.json' ).name;
+var izamax = require( './../lib/izamax.js' );
+
+
+// VARIABLES //
+
+var options = {
+'dtype': 'float64'
+};
+
+
+// FUNCTIONS //
+
+/**
+* Create a benchmark function.
+*
+* @private
+* @param {PositiveInteger} len - array length
+* @returns {Function} benchmark function
+*/
+function createBenchmark( len ) {
+var zx;
+
+zx = new Complex128Array( uniform( len*2, -100.0, 100.0, options ) );
+return benchmark;
+
+/**
+* Benchmark function.
+*
+* @private
+* @param {Benchmark} b - benchmark instance
+*/
+function benchmark( b ) {
+var idx;
+var i;
+
+b.tic();
+for ( i = 0; i < b.iterations; i++ ) {
+idx = izamax( zx.length, zx, 1 );
+if ( isnan( idx ) ) {
+b.fail( 'should not return NaN' );
+}
+}
+b.toc();
+if ( isnan( idx ) ) {
+b.fail( 'should not return NaN' );
+}
+b.pass( 'benchmark finished' );
+b.end();
+}
+}
+
+
+// MAIN //
+
+/**
+* Main execution sequence.
+*
+* @private
+*/
+function main() {
+var len;
+var min;
+var max;
+var f;
+var i;
+
+min = 1; // 10^min
+max = 6; // 10^max
+
+for ( i = min; i <= max; i++ ) {
+len = pow( 10, i );
+f = createBenchmark( len );
+bench( pkg+':len='+len, f );
+}
+}
+
+main();
@@ -0,0 +1,105 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2025 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var bench = require( '@stdlib/bench' );
+var uniform = require( '@stdlib/random/array/uniform' );
+var isnan = require( '@stdlib/math/base/assert/is-nan' );
+var pow = require( '@stdlib/math/base/special/pow' );
+var Complex128Array = require( '@stdlib/array/complex128' );
+var pkg = require( './../package.json' ).name;
+var izamax = require( './../lib/ndarray.js' );
+
+
+// VARIABLES //
+
+var options = {
+'dtype': 'float64'
+};
+
+
+// FUNCTIONS //
+
+/**
+* Create a benchmark function.
+*
+* @private
+* @param {PositiveInteger} len - array length
+* @returns {Function} benchmark function
+*/
+function createBenchmark( len ) {
+var zx;
+
+zx = new Complex128Array( uniform( len*2, -100.0, 100.0, options ) );
+return benchmark;
+
+/**
+* Benchmark function.
+*
+* @private
+* @param {Benchmark} b - benchmark instance
+*/
+function benchmark( b ) {
+var idx;
+var i;
+
+b.tic();
+for ( i = 0; i < b.iterations; i++ ) {
+idx = izamax( zx.length, zx, 1, 0 );
+if ( isnan( idx ) ) {
+b.fail( 'should not return NaN' );
+}
+}
+b.toc();
+if ( isnan( idx ) ) {
+b.fail( 'should not return NaN' );
+}
+b.pass( 'benchmark finished' );
+b.end();
+}
+}
+
+
+// MAIN //
+
+/**
+* Main execution sequence.
+*
+* @private
+*/
+function main() {
+var len;
+var min;
+var max;
+var f;
+var i;
+
+min = 1; // 10^min
+max = 6; // 10^max
+
+for ( i = min; i <= max; i++ ) {
+len = pow( 10, i );
+f = createBenchmark( len );
+bench( pkg+':ndarray:len='+len, f );
+}
+}
+
+main();